Summary (refrigeration and air conditioning )

SUMMARY■ Thermometers measure temperature. Four temperature scalesare Fahrenheit, Celsius, Fahrenheit absolute (Rankine), andCelsius absolute (Kelvin).■ Molecules in matter are constantly moving. The higher thetemperature, the faster they move.■ The British thermal unit (Btu) describes the quantity of heatin a substance. One Btu is the amount of heat necessary toraise the temperature of 1 lb of water 1°F.■ The transfer of heat by conduction is the transfer of heat frommolecule to molecule. As molecules in a substance movefaster and with more energy, they cause others near them todo the same.■ The transfer of heat by convection is the actual moving ofheat in a fluid (vapor state or liquid state) from one place toanother.■ Radiant heat is a form of energy that does not depend on matteras a medium of transfer. Solid objects absorb the energy,become heated, and transfer the heat to the air.■ Sensible heat causes a rise in temperature of a substance.■ Latent (or hidden) heat is that heat added to a substance causinga change of state and not registering on a thermometer.For example, heat added to melting ice causes ice to melt butdoes not increase the temperature.■ Specific heat is the amount of heat (measured in Btu) requiredto raise the temperature of 1 lb of a substance 1°F.Substances have different specific heats.■ Pressure is the force applied to a specific unit of area. The atmospherearound the earth has weight and therefore exertspressure.■ Barometers measure atmospheric pressures in inches of mercury.Two barometers used are the mercury and the aneroid.■ Gages have been developed to measure pressures in enclosedsystems. Two common gages used in the air-conditioning,heating, and refrigeration industry are the compound gage and the high-pressure gage. The compound gage reads pressures both above and below atmospheric pressure.■ The metric term kilopascal (kPa) is used to express pressurein the refrigeration and air-conditioning field.

SUMMARY■ Matter takes up space, has mass, and can be in the form of asolid, a liquid, or a gas.■ The weight of a substance at rest on the earth is proportionalto its mass.■ In the British system of units, density is the weight of a substanceper cubic foot.■ Specific gravity is the term used to compare the density ofvarious substances.■ Specific volume is the amount of space a pound of a vapor ora gas will occupy.■ Boyle’s Law states that the volume of a gas varies inverselywith the absolute pressure, provided the temperature remainsconstant.■ Charles’ Law states that at a constant pressure, the volume ofa gas varies directly as to the absolute temperature, and at aconstant volume the pressure of a gas varies directly with theabsolute temperature.■ Dalton’s Law states that the total pressure of a confined mixture

of gases is the sum of the pressures of each of the gasesin the mixture.■ Electrical energy and heat energy are two forms of energyused in this industry.■ Fossil fuels are purchased by the unit. Natural gas is meteredby the cubic foot; oil is purchased by the gallon; and coal ispurchased by the ton. Electricity is purchased from the electricutility company by the kilowatt-hour (kWh).■ Work is the amount of force necessary to move an object:Work _ Force _ Distance.■ Horsepower is the equivalent of lifting 33,000 lb to a heightof 1 ft in 1 min or some combination totaling the same.■ Watts are a measurement of electrical power. One horsepowerequals 746 W.■ 3.413 Btu _ 1 W. 1 kW (1000 W) _ 3413 Btu.

SUMMARY■ Bacterial growth that causes food spoilage slows at lowtemperatures.■ Product temperatures above 45°F and below room temperatureare considered high-temperature refrigeration.■ Product temperatures between 35°F and 45°F are consideredmedium-temperature refrigeration.■ Product temperatures from 0°F to _10°F are consideredlow-temperature refrigeration.■ Refrigeration is the process of removing heat from a placewhere it is not wanted and transferring it to a place where itmakes little or no difference.■ One ton of refrigeration is the amount of heat necessary to melt1 ton of ice in a 24-hour period. It takes 288,000 Btu to melt1 ton of ice in a 24-hour period or 12,000 Btu in 1 h or 200 Btuin 1 min.■ The relationship of the vapor pressure and the boilingpoint temperature is called the temperature/pressurerelationship.■ A compressor can be considered a vapor pump. It lowers thepressure in the evaporator to the desired temperature andincreases the pressure in the condenser to a level where thevapor may be condensed to a liquid.■ The liquid refrigerant moves from the condenser to themetering device where it again enters the evaporator.■ Refrigerants have a definite chemical makeup and are usuallydesignated with an “R” and a number for field identification.■ A refrigerant must be safe, must be detectable, must be environmentallyfriendly, must have a low boiling point, andmust have good pumping characteristics.■ Refrigerant cylinders are color coded to indicate the typeof refrigerant they contain.■ Refrigerants should be recovered or stored while a refrigerationsystem is being serviced, then recycled, if appropriate,or sent to a manufacturer to be reclaimed.■ Pressure/enthalpy diagrams may be used to plot refrigerationcycles.

SUMMARY■ The technician must use every precaution when workingwith pressures, electrical energy, heat, cold, rotating machinery,and chemicals, and when moving heavy objects.■ Technicians encounter safety situations involving pressure

while working with pressurized systems and vessels.■ Electrical energy is present whenever you troubleshootenergized electrical circuits. Be careful. Turn off electricalpower, if possible, when working on an electrical component.Lock the panel or disconnect the box and keep the onlykey in your possession.■ Refrigerant-specific leak detectors that sense parts per million(PPM) of refrigerant are used in equipment rooms forsafety.■ Some fire extinguishers are designed for specific types offires, and some can be used for many types: trash, wood,paper, liquid, and electrical fires.■ Evacuation plans and building directories mounted in a conspicuousplace on the building’s interior walls are an importantsafety feature.■ Heat is encountered during soldering and when heating systemsare being worked on.■ Liquid R-22 refrigerant boils at _41°F at atmospheric pressureand will cause frostbite.■ Rotating equipment such as fans and pumps can be dangerousand should be treated with caution.■ When moving heavy equipment, use correct techniques,choose appropriate tools and equipment, and wear a backbrace belt.■ Chemicals are used for cleaning and water treatment andmust be handled with care.

SUMMARY■ Air-conditioning, heating, and refrigeration techniciansshould be familiar with available hand tools and equipment.■ Technicians should properly use hand tools and specializedequipment.■ SAFETY PRECAUTION: These tools and this equipmentshould be used only for the job for which they were designed.Other use may damage the tool or equipment andmay be unsafe for the technician.

SUMMARY■ Technicians need to use a broad variety of fasteners.■ Some of these fasteners are nails, screws, staples, tappingscrews, and set screws.■ Anchor shields and other devices are often used with screwsto secure them in masonry walls or hollow walls.■ Typical hangers used with pipe, tubing, and ductwork arewire pipe hooks, pipe straps, perforated steel straps, and customhangers made from threaded rod and angle steel.■ Other specialty fasteners are available for flexible duct andfiberglass duct.■ Solder-less terminals are used to fasten wire to terminals.■ Screw-on wire connectors are used to fasten two or morelengths of wire together.

SUMMARY■ The use of correct tubing, piping, and fittings—as well astheir proper installation—is necessary in order for a refrigerationor air-conditioning system to operate properly. Carelesshandling of the tubing and poor soldering or brazingtechniques may cause serious damage to the components ofthe system.■ Copper tubing is generally used for plumbing, heating, and

refrigerant piping.■ Copper tubing is available in soft- or hard-drawn copper.■ ACR tubing can be purchased as line sets.■ Tubing may be cut with a hacksaw or tubing cutter.■ Soft tubing may be bent. Tube-bending springs or lever-typebenders may be used, or the bend can be made by hand.■ Soldering and brazing fasten tubing and fittings together.■ Air-acetylene units are frequently used for soldering andbrazing.■ Oxyacetylene equipment is also used, particularly for brazingrequiring higher temperatures.■ The flare joint is another method of joining tubing andfittings.■ The soldered swaged joint is a method used to fasten twopieces of copper tubing together.■ Steel pipe is used in plumbing, hydronic heating, and gasheating applications.■ Steel pipe is joined with threaded fittings or by welding.■ ABS, PE, PVC, and CPVC are four types of plastic pipe;each has a different use.■ Alternative mechanical piping-connection methods can beused for certain applications.

SUMMARY■ Nitrogen and R-22 (used as a trace refrigerant for findingleaks) are commonly used to leak check a system.■ Using R-22 as a trace refrigerant is approved, because it isnot used as an operating refrigerant.■ The entire system must not be pressurized higher than thelowest system test pressure.■ While under pressure, the system can be leak checked usingseveral different methods: halide, soap, ultrasonic, andelectronic.■ It is not required by the Environmental Protection Agency torepair systems that contain less than 50 lb of refrigerant. Forindustrial processes equipment and commercial refrigerationequipment, systems that contain more than 50 lb ofrefrigerant must be repaired when the leak rate is more than35% of their total charge in 1 year. An annual leak rateof 15% is allowed for comfort cooling chillers and all otherequipment.■ Non-condensable gases and moisture are common foreignmatter that get into systems during assembly and repair. Theymust be removed.■ Evacuation using low vacuum levels removes non-condensablegases and involves pumping the system to below atmosphericpressure.■ Vapors will be pumped out by the vacuum pump. Liquidsmust boil to be removed with a vacuum.■ Water makes a large volume of vapor when boiled atlow pressure levels. It should be drained from a system ifpossible.■ The two common vacuum gages are the U-tube manometerand the electronic micron gage.■ Pumping a vacuum may be quickened with large unrestrictedlines.■ Good workmanship and piping practice along with a drynitrogen setup will lessen the evacuation time.■ When non-condensables are left in a system, mild acids (hydrochloric

and hydrofluoric) will slowly form and deterioratethe system by attacking the motor windings and causingcopper plating on the crankshaft.■ The oxygen in the air is the real problem when air is allowedto enter a system.■ Nitrogen in a system will cause excess head pressure becauseit takes up condensing space.■ The best system pressure test is a standing pressure test,normally 150 psig.■ The only advantage in using a vacuum to test for leaks is thatvacuum instruments quickly respond to leaks. The vacuumleak test only proves that the system piping will preventatmosphere from entering the system (14.969 psi).■ When a vacuum pump is allowed to run unattended, the systembecomes a large vacuum reservoir—and if the vacuumpump were to be shut off, the oil will be pulled into the system.If the vacuum pump is then restarted, it will be operatingwithout lubrication.■ Special valve arrangements allow the technician to check thevacuum gage and pump and also check the system pressure.■ System Schrader valve cores may be removed to quicken thevacuum on a system; then the cores may be replaced beforethe system is put back in operation.■ Using dry nitrogen to sweep a contaminated system will helpin evacuating a dirty system.■ Do not forget to clean the vacuum pump after evacuating acontaminated system.

SUMMARY■ CFC refrigerants must not be vented to the atmosphere.■ Ozone is a form of oxygen, with each molecule consisting ofthree atoms of oxygen (O3). The oxygen we breathe containstwo atoms (O2).■ The ozone layer, located in the stratosphere 7 to 30 milesabove the earth’s surface, protects the earth from harmfulultraviolet rays from the sun, which can cause damage tohuman beings, animals, and plants.■ Ozone Depletion Potentials (ODPs) have been establishedby the Montreal Protocol.■ Global warming is a process that takes place in the loweratmosphere, or troposphere.■ Both direct and indirect effects of global warming exist.■ Global warming potentials (GWPs) are given to refrigerants.■ Chlorofluorocarbons (CFCs) contain chlorine, fluorine, andcarbon atoms.■ Hydrochlorofluorocarbons (HCFCs) contain hydrogen,chlorine, fluorine, and carbon atoms.■ Hydrofluorocarbons (HFCs) contain hydrogen, fluorine, andcarbon atoms.■ Some hydrocarbons (HCs) are entering the markets as part ofrefrigerant blends.■ Both zeotropic and azeotropic refrigerant blends havebecome very popular as replacements for both CFC andHCFC refrigerants.■ Both near-azeotropic and zeotropic blends exhibit temperatureglide and fractionation when they evaporate andcondense.■ Refrigerant oils have been researched extensively because ofthe refrigerant transition.

■ Synthetic oils have gained popularity and are being used witha lot of the newer refrigerants.■ Refrigerant and oil retrofitting guidelines have been establishedfor service purposes because of the refrigerant and oiltransition.■ Hydrogen atoms help the HCFCs break down before theyreach the stratosphere and react with the ozone.■ The EPA has established many regulations governing thehandling of refrigerants.■ To recover refrigerant is “to remove refrigerant in any conditionfrom a system and store it in an external container withoutnecessarily testing or processing it in any way.”■ To recycle refrigerant is “to clean the refrigerant by oil separationand single or multiple passes through devices, suchas replaceable core filter-driers, which reduce moisture, acidity,and particulate matter. This term usually applies to proceduresimplemented at the job site or at a local serviceshop.”■ To reclaim refrigerant is “to process refrigerant to new productspecifications by means which may include distillation.It will require chemical analysis of the refrigerant to determinethat appropriate product specifications are met. Thisterm usually implies the use of processes or procedures availableonly at a reprocessing or manufacturing facility.”■ Active recovery involves recovering refrigerant through theuse of a certified self-contained recovery machine.■ Passive recovery or system-dependent recovery is when theservice technician uses the internal pressure of the systemand/or the system’s compressor to aid in the refrigerantrecovery process.■ Recovery of small appliances involves the use of differentmethods and different evacuation levels.■ Refrigerant can be transferred only into Department ofTransportation (DOT)–approved cylinders and tanks.■ Manufacturers have developed many types of equipment torecover and recycle refrigerant.

SUMMARY■ Refrigerant may be added to the refrigeration system in thevapor state or the liquid state under proper conditions.■ When refrigerant is added in the vapor state, the refrigerantcylinder will lose pressure as the vapor is pushed out of thecylinder.■ Liquid refrigerant is normally added in the liquid line andonly under the proper conditions.■ Liquid refrigerant must come out of the charging cylinderwhen the technician is charging with certain refrigerantblends. This will avoid fractionation. Once out of the chargingcylinder, this liquid must be restricted and vaporized toavoid liquid refrigerant from entering the compressor.■ Liquid refrigerant must never be allowed to enter thecompressor.■ Refrigerant is measured into systems using weight andvolume.■ It can be difficult to add refrigerant with dial scales becausethe final cylinder weight must be calculated. The scales aregraduated in pounds and ounces.■ Electronic scales may have a cylinder-emptying feature thatallows the scales to be adjusted to zero with a full cylinder of

refrigerant on the platform.■ Graduated cylinders use the volume of the liquid refrigerant.This volume varies at different temperatures. These may bedialed onto the cylinder for accuracy.■ Near-azeotropic or zeotropic blends have entered the refrigerationand air-conditioning industry with the onset of theozone-depletion and global-warming scares.■ Zeotropic blends can exhibit temperature glide (when phasechanging) and fractionation (when vapor leaking or chargingas a vapor).■ All zeotropic blends must come out of the charging cylinderas a liquid to avoid fractionation.■ Some sort of restricting device must be used with zeotropicblends when charging to vaporize the liquid refrigerant beforeit enters the compressor.■ Manufacturer charging charts and curves can assist the servicetechnician in correctly charging an accurate amount ofrefrigerant into an air-conditioning or heat pump system.■ The subcooling method of refrigerant charging is used on airconditioningand heat pump systems incorporating a thermostaticexpansion valve for a metering device.■ Manufacturers have designed new pressure/temperaturecharts that make it easier for service technicians to check asystem for the right amount of refrigerant charge when dealingwith near-azeotropic refrigerant blends that have a temperatureglide.

SUMMARY■ Reference points for all instruments should be established togive the technician confidence.■ The three easily obtainable reference points for temperaturemeasuringinstruments are ice and water at 32°F, body temperatureat 98.6°F, and boiling temperature at 212°F.■ Make sure that the temperature-sensing element reflects theactual temperature of the medium used as the standard.■ Pressure-measuring instruments must be checked above andbelow atmospheric pressure. There are no good referencepoints below the atmosphere, so a vacuum pump pulling adeep vacuum is used as the reference.■ Flue-gas analysis kits need no calibration except for the slidingscale on the sample chamber.

SUMMARY■ Atoms are made up of protons, neutrons, and electrons.■ Protons have a positive charge, and electrons have a negativecharge.■ Electrons travel in orbits around the protons and neutrons.■ When a surplus of electrons is in an atom, it has a negativecharge. When a deficiency of electrons exists, the atom has apositive charge.■ Electricity can be produced by using magnetism. A conductorcutting through magnetic lines of force produceselectricity.■ Direct current (DC) is an electrical current moving in onedirection.■ Alternating current (AC) is an electrical current that is continuallyreversing.■ Volt _ electrical force or pressure.■ Ampere _ quantity of electron flow.

■ Ohm _ resistance to electron flow.■ Voltage (E) _Amperage (I) _Resistance (R). This is Ohm’slaw.■ In series circuits the voltage is divided across the resistances,the total current flows through each resistance, and the resistancesare added together to obtain the total resistance.■ In parallel circuits the total voltage is applied across each resistance,the current is divided between the resistances, andthe total resistance is less than that of the smallest resistance.■ Electrical power is measured in watts, P _ E _ I.■ Inductive reactance is the resistance caused by the magneticfield surrounding a coil in an AC circuit.■ A step-up transformer increases the voltage and decreasesthe current. A step-down transformer decreases the voltageand increases the current.■ A capacitor in an AC circuit will continually charge and dischargeas the current in the circuit reverses.■ A capacitor has capacitance, which is the amount of chargethat can be stored.■ Impedance is the opposition to current flow in an AC circuitfrom the combination of resistance, inductive reactance, andcapacitive reactance.■ A multimeter often used is the VOM (volt-ohmmilliammeter).■ A sine wave displays the voltage of one AC cycle through360°.■ SAFETY PRECAUTION: Properly sized conductors mustbe used. Larger wire sizes will carry more current thansmaller wire sizes without overheating.■ SAFETY PRECAUTION: Fuses and circuit breakers areused to interrupt the current flow in a circuit when thecurrent is excessive.■ Semiconductors in their pure state do not conduct electricitywell, but when they are doped with an impurity, they form anN-type or P-type material that will conduct in one direction.■ Diodes, rectifiers, transistors, thermistors, diacs, and triacsare examples of semiconductors.

SUMMARY■ A bimetal element is two unlike metal strips such as brassand steel fastened back to back.■ Bimetal strips warp with temperature changes and can beused to stop, start, or modulate electrical current flow andfluid flow when used with different mechanical, electrical,and electronic helpers.■ The travel of the bimetal can be extended by coiling it. Thehelix, worm shape, hairpin shape, and coil are the namesgiven on the extended bimetal.■ The rod and tube is another version of the bimetal.■ Fluid expansion is used in the thermometer to indicate temperatureand to operate controls that are totally liquid filled.■ The temperature/pressure relationship is applied to somecontrols that are partially filled with liquid.■ The diaphragm is used to move the control mechanism wheneither liquid or vapor pressure is applied to it.■ The diaphragm has very little travel but much power.■ The bellows is used for more travel and is normally vaporfilled.■ The Bourdon tube is sometimes used like the diaphragm or

bellows.■ The thermocouple generates electrical current flow whenheated at the hot junction.■ This current flow can be used to monitor temperaturechanges to stop, start, or modulate electrical circuits.■ The thermistor is an electronic device that varies its resistanceto electrical current flow on the basis of temperature changes.■ Positive temperature coefficient (PTC) thermistors increasein resistance as the temperature increases. Negative temperaturecoefficient (NTC) thermistors decrease in resistancewhen the temperature increases.

SUMMARY■ Space temperature controls can be either low-voltage or linevoltagetypes.■ Low voltage is normally applied to residential heating andcooling controls.■ Heating thermostats normally have a heat anticipator circuitin series with the thermostat contacts.■ Cooling thermostats may have a cooling anticipator in parallelwith the thermostat contacts.■ Line-voltage thermostats are normally rated up to 20 A ofcurrent because they are used to switch high-voltage current.■ Low-voltage thermostats normally will carry only 2 A ofcurrent.■ To get a correct temperature reading of a flat or round surface,the sensing element (either mercury bulb, remote bulb,or bimetal) must be in good contact with the surface andinsulated from the ambient air.■ Some installations have wells in the substance to be sensedin which the sensor can be placed.■ Motors have both internal and external types of motortemperature-sensing devices.■ The internal type of motor temperature-sensing device canbe either a bimetal or a thermistor inserted inside the motorwindings.■ Some sensing elements are inserted into the fluid stream. Examplesare the fan or limit switch on a gas, oil, or electricfurnace.■ All temperature-sensing elements change in some mannerwith a change in temperature: the bimetal warps, the thermistorchanges resistance, and the thermocouple changes voltage.■ Pressure controls normally are either diaphragm, Bourdontube, or bellows operated.■ Pressure controls can operate at high pressures, low pressures,and even below atmospheric pressure (in a vacuum),and can detect differential pressures.■ SAFETY PRECAUTION: Gas pressure must be reduced beforeit enters a house or place of business to be burned inan appliance.■ Some purely mechanical controls are water-regulatingvalves, pressure relief valves, and expansion valves.■ Some electromechanical controls are low-pressure cut-out,high-pressure cut-out, and thermostats.■ Keep and study manufacturers’ literature.

SUMMARY■ Each control must be evaluated as to its purpose in a circuit.■ Electrical controls are divided into two categories: powerconsuming

and power-passing (non–power consuming).■ One method of understanding a circuit is that the power supplyis the potential difference between two power legs.■ Devices or controls that pass power are known as safety,operating, or control devices.■ The light bulb controlled by a thermostat with a fuse inthe circuit is an example of an operating device and a safetydevice in the same circuit.■ The voltmeter may be used to follow the circuit from thebeginning to the power-consuming device.■ The three separate power-consuming circuits in the lowvoltagecontrol of a typical heating and cooling fan unit are theheat circuit, cool circuit, and fan circuit. The selector switchfor heating and cooling decides which function will operate.■ The fan relay, cooling relay, and heat relay are all powerconsumingdevices.■ The low-voltage relays start the high-voltage powerconsumingdevices.■ The voltmeter is used to trace the actual voltage at variouspoints in the circuit.■ The ohmmeter is used to check for continuity in a circuit.■ The ammeter is used to detect current flow.■ The pictorial diagram has wire colors and destinationsprinted on it. It shows the actual locations of all components.■ The line or ladder diagram is used to trace the circuit andunderstand its purpose.

SUMMARY■ Automatic controls are a big part of all modern buildings.■ The industry technician should be able to look at and interpretbuilding blueprints and their control circuits.■ Modern control systems use modulating controls as well ason–off control systems.■ Control systems can be subdivided into control loops forbetter understanding.■ A basic control loop has a sensor, controller, and somethingto be controlled.■ In a home air-conditioning system the thermostat is the sensor,the contactor is the controller, and the compressor (andfans) is the controlled device.■ Pneumatic controls are typically used in commercial applicationsand are mechanical in nature. They use air pressureinstead of electricity to position the system devices.■ Pneumatic controls are explosion-proof, simple, safe, andreliable.■ The air that operates pneumatic controls is typically 0 to20 psig and must be clean and dry.■ Air pressure is amplified for more power using diaphragmsof a large size.■ Diaphragm mechanisms with a plunger may be used tooperate dampers and valves to modulate the flow of fluids(air, water, and refrigerant) to control room and buildingconditions.■ Since pneumatic controls use air, they can often be heardrepositioning as the air bleeds from the control.■ A pilot positioner is often used on the controlled device tohandle large volumes of air needed to fill or exhaust a largediaphragm.■ The tools of the pneumatic technician are an air gage, thermometer,

and special wrench (usually Allen type).■ Direct digital control (DDC) is a control process in whicha microprocessor, acting as a digital controller, constantlyupdates a database of internal information. Through sensors,the microprocessor updates this information by watchingand monitoring information from an external controlled environmentor conditioned space. The microprocessor thencontinually produces corrections and outputs this correctedinformation back to the controlled environment.■ Direct digital controls, called DDCs, are an electronicversion of pneumatic controls, only they are much moreversatile.■ Computers are used to create logic with these control systems,and many more features and control points can becoordinated together.■ DDCs and pneumatic controls may be used together; therefore,older systems can be updated with DDC systems.■ Modern electronic controls have been developed, tried, andproven in commercial systems and are now being used formany residential applications.■ The residential technician does not have to be an electronictechnician to troubleshoot the system. Many of these systemshave built-in diagnostics.■ The electronics control temperature, humidity, air, andrefrigerant flow in residential systems.

SUMMARY■ Motors turn fans, compressors, and pumps.■ Some of these applications need high starting torque andgood running efficiencies; some need low starting torquewith average or good running efficiencies.■ Compressors applied to refrigeration normally require motorswith high starting torque.■ Small fans normally need motors that have low startingtorque.■ The voltage supplied to a particular installation will determinethe motor’s voltage. The common voltage for furnacefans is 115 V; 230 V is the common voltage for home airconditioningsystems.■ Common single-phase motors are split-phase, PSC, andshaded-pole.■ When more starting torque is needed, a start capacitor isadded to the motor.■ A run capacitor improves the running efficiency of the splitphasemotor.■ A centrifugal switch breaks the circuit to the start windingwhen the motor is up to running speed. The switch changesposition with the speed of the motor.■ An electronic switch may be used to interrupt power to thestart winding.■ The common rated speed of a single-phase motor is determinedby the number of poles or windings in the motor. The commonspeeds are 1800 rpm, which will slip in speed to about1725 rpm, and 3600 rpm, which will slip to about 3450 rpm.■ The difference between 1800_3600 and the running speedsof 1750_3450 is known as the slip. Slip is due to the loadimposed on the motor while operating.■ Three-phase motors are used for all large applications. They

have a high starting torque and a high running efficiency. Three-phase power is not available at most residences, so thesemotors are limited to commercial and industrial installations.■ The power to operate hermetic motors must be conductedthrough the shell of the compressor by way of insulatedmotor terminals.■ Since the winding of a hermetic compressor is in the refrigerantatmosphere, a centrifugal switch may not be used tointerrupt the power to the start winding.■ A potential relay takes the start winding out of the circuitusing BEMF.■ A current relay breaks the circuit to the start winding usingthe motor’s run current.■ The PSC motor is used when high starting torque is not required.It needs no starting device other than the run capacitor.■ The PTC device is used with some PSC motors to give smallamounts of starting torque. It has no moving parts.■ When compressors are larger than 5 tons, they are normallythree-phase.■ Dual-voltage three-phase compressors are built with twomotors wired into the housing.■ Three-phase reciprocating compressors come in sizes up toabout 125 tons.■ Variable-speed motors operate at higher efficiencies withvarying loads.■ The electronically commutated motor (ECM) is a DC motorthat does not have brushes.■ Variable-speed motors can even out the load on the heatingand air-conditioning systems by adjusting the equipmentspeed to the actual load.■ Motor speed can be varied from about 10% of rated speed toabout 120% using electronics.■ Electronic switches, silicon-controlled rectifiers (SCRs), andtransistors can be turned on and off without making an arc.They are reliable and do not use much power.■ DC converters convert AC power to DC power.■ Capacitors even out the pulsating DC power.■ Inverters create an alternating frequency that can be varied.■ The frequency and the voltage must be changed together forthe motor to perform efficiently.

SUMMARY■ In many installations only one type of motor can be used.■ The power supply determines the applied voltage, the currentcapacity, the frequency, and the number of phases.■ The working conditions (duty) for a motor specify the atmospherein which the motor must operate (i.e., wet, explosive,or dirty).■ Motors are also classified according to the insulation of themotor windings and the motor temperature under which theyoperate.■ Each motor has sleeve, ball, or roller bearings. Sleeve bearingsare the quietest but will not stand heavy loads.■ SAFETY PRECAUTION: Motors must be mounted in thefashion designed for the installation.■ SAFETY PRECAUTION: An exact motor replacementshould be obtained whenever possible.■ The drive mechanism transfers the motor’s energy to the

driven device (the fan, pump, or compressor).

SUMMARY■ The relay, the contactor, and the motor starter are three typesof motor starting and stopping devices.■ The relay is used for switching circuits and motor starting.■ Motor starting relays are used for heavier duty jobs than areswitching relays.■ Contactors are large relays that may be rebuilt.■ Starters are contactors with motor overload protection builtinto the framework of the contactor.■ The contacts on relays, contactors, and starters should not befiled or sanded.■ Large motors should be protected from overload conditionsthrough the use of devices other than normal circuit overloadprotection devices.■ Inherent motor overload protection is provided by sensingdevices within the motor.■ External motor overload protection is applied to the currentpassingdevice: the relay, the contactor, or the starter.■ The service factor is the reserve capacity of the motor.■ Bimetal and solder-pot devices are thermally operated.■ Magnetic overload devices are very accurate and not affectedby ambient temperature.■ SAFETY PRECAUTION: Most motors should not berestarted immediately after shutdown from an overloadcondition because they may need time to cool. When possible,determine the reason for the overload condition beforerestarting the motor.

SUMMARY■ Bearing problems are often caused by belt tension.■ Shaft problems may be caused by the technician while he orshe is removing pulleys or couplings.■ Motor balancing problems are normally not handled by theheating, air-conditioning, and refrigeration technician.■ Make sure that vibration is not caused by the system.■ Most electrical problems are open windings, short-circuitedwindings, or grounded windings.■ The laws of electrical current flow must be used when troubleshootingmotors.■ If the motor is receiving the correct voltage and is electricallysound, check the motor components.■ Troubleshooting hermetic compressor motors is differentfrom troubleshooting open motors because hermetic motorsare enclosed.

SUMMARY■ Heat travels normally from a warm substance to a coolsubstance.■ For heat to travel from a cool substance to a warm substance,work must be performed. The motor that drives the compressorin the refrigeration cycle does this work.■ The evaporator is the component that absorbs the heat intothe refrigeration system.■ The evaporator must be cooler than the medium to be cooledto have a heat exchange.■ The refrigerant boils to a vapor in the evaporator and absorbsheat because it is boiling at a low pressure and low

temperature.■ The boiling temperature of the refrigerant in the evaporatordetermines the evaporator (low-side) pressure.■ Medium-temperature systems can use off-cycle defrost. Theproduct is above freezing, and the heat from it can be used tocause the defrost.■ Low-temperature refrigeration must have heat added to theevaporator to melt the ice.■ Evaporators have the same characteristics for the same typesof installations regardless of location.■ Most refrigeration coils are copper with aluminum fins.■ The starting point in organized troubleshooting is to determinewhether the evaporator is operating efficiently.■ Checking the superheat is the best method the service technicianhas for evaluating evaporator performance.■ Some evaporators are called dry-type because they use aminimum of refrigerant.■ Dry-type evaporators are also called direct-expansionevaporators.■ Some evaporators are flooded and use a float to meter therefrigerant. Superheat checks on these evaporators shouldbe interpreted with caution.■ Some evaporators have a single circuit, and some have multiplecircuits.■ Multicircuit evaporators keep excessive pressure drop fromoccurring in the evaporator.■ There is a relationship between the boiling temperature ofthe refrigerant in the evaporator and the temperature of themedium being cooled.■ The coil normally operates at temperatures from 10°F to 20°Fcolder than the temperature of the air passing over it.

SUMMARY■ The condenser is the component that rejects the heat from therefrigeration system.■ The refrigerant condenses to a liquid in the condenser andgives up heat.■ Water is the first medium that heat is rejected into throughthe water-cooled condenser.■ There are three types of water-cooled condensers: the tubewithin a tube, the shell and coil, and the shell and tube.■ The greatest amount of heat is given up from the refrigerantwhile the condensing process is taking place.■ The refrigerant normally condenses about 10°F higher thanthe leaving condensing medium in a water-cooled condenserthat uses a cooling tower.■ The first job of the condenser is to desuperheat the gas flowingfrom the compressor.■ After the refrigerant is condensed to a liquid, the liquid canbe further cooled below the condensing temperature. This iscalled subcooling.■ When the condensing medium is cold enough to reduce thehead pressure to the point that the expansion device willstarve the evaporator, a head pressure control must be used,whether air or water is being used as the condensingmedium.

■ The three types of cooling towers are natural draft, forceddraft, and evaporative.

■ Recirculated water uses evaporation to help the coolingprocess.■ When water is evaporated, it will overconcentrate the minerals,and water must be added to the system to keep this fromhappening.■ Four types of common head pressure controls are fancyclingcontrols, variable-speed fans, shutters, and condenserflooding controls.■ The relationship of the condensing temperature to the temperatureof the air passing over a condenser can help the servicetechnician determine what the high-pressure gagereading should be on air-cooled condensers.

SUMMARY■ The compressor is a vapor pump.■ The compressor lifts the low-pressure gas from the suctionside of the system to the discharge side of the system.■ The discharge gas can be quite hot because the heat containedin the cool suction gas is concentrated when compressedin the compressor.■ Additional heat is added to the gas as it passes through thecompressor because some of the work energy does not convertdirectly to compression but converts to heat.■ Three types of compressors are usually used to achievecompression in commercial refrigeration: the reciprocating,rotary screw, and scroll compressor.■ Hermetic and open-drive are two types of reciprocatingcompressors.■ Hermetic compressors are manufactured as welded hermeticand serviceable hermetic.■ The welded hermetic compressor must have the shell cutopen for it to be serviced, and this work is done by specialrebuilding shops only.■ In the serviceable hermetic compressor the shell is boltedtogether and can be disassembled in the field.■ Most reciprocating compressor motors are cooled by suctiongas. Some are air cooled.■ In all hermetic compressors the motor is operating in therefrigerant atmosphere and special precautions must be takenin the manufacture and service of these motors.■ Hermetic compressors have a shaft with the motor on oneend and the compressor on the other end.■ Special internal overload devices are used on hermetic motorsthat operate inside the refrigerant atmosphere.■ One type of internal overload protection device interrupts theactual line current. If this overload device does not closeback when it should, the compressor is defective.■ The other internal overload device is a pilot-duty type thatinterrupts the control voltage. If something were to happento this device, an external type could be installed.■ Some compressors use thermistors in or near the motorwindings to sense motor heat. The thermistors are then wiredto a solid-state electronic compressor protection module,which will decide when the compressor should be cycled offbecause of excessive heat.■ Reciprocating compressors are positive displacement pumps,meaning that when they have a cylinder full of gas or liquid,the cylinder is going to be emptied, or damage will occur.■ With open compressors the motor is on the outside of the

system.■ The motor can be mounted beside the compressor, the compressorand motor shafts may be side by side, or the motormay be mounted at the end of the compressor shaft with aflexible coupling between them.■ Shaft-to-motor alignment is very important.■ Belts for belt-drive applications come in different types. Themanufacturer’s supplier should be consulted for advice.■ Discus valve design provides for smaller clearance volume,a greater area through which the gas can flow, and consequentlygreater efficiency.■ Continued compressor efficiencies depend to a great extenton a good maintenance program.

SUMMARY■ The expansion device is one of the dividing points betweenthe high and low sides of the system.■ The TXV valve maintains a constant superheat in the evaporator.■ The bulb pressure is the only force that acts to open the valve.■ The forces inside the expansion valve all work together tohold the needle and seat in the correct position so that theevaporator will have the correct amount of refrigerant underall load conditions.■ The liquid temperature entering the TXV, the evaporatortemperature, and the pressure drop across the TXV all determinethe capacity of the TXV in tons.■ Balanced-port TXVs are used where low ambient temperaturesexist, head pressures vary widely, evaporator loads varywidely, large pressure drops exist across the TXV, or lowliquid-line temperatures exist.■ Maximum operating pressure (MOP) TXVs limit the evaporatingpressure to prevent the compressor from overloading.■ The solid-state controlled expansion valve uses a thermistorto monitor the evaporator outlet temperature to controlrefrigerant flow to the evaporator.■ Electronic expansion valves (EEVs) use either heat motorsor step motors for valve movement.■ EEVs use proportional, integral, and derivative (PID) controllersfor their operations.■ The automatic expansion valve responds in reverse to a loadchange; when the load increases, the automatic expansionvalve throttles the refrigerant instead of feeding more refrigerantas the TXV does.■ The capillary tube expansion device is a fixed-bore meteringdevice usually made of copper, with a very small insidediameter and no moving parts.■ The capillary tube system uses a very limited amount ofrefrigerant compared with other metering devices and ispopular for small systems.

SUMMARY■ Four basic components of the compression cycle are thecompressor, condenser, evaporator, and expansion device.■ Two other types of components that enhance the refrigerationcycle are control components and accessories.■ Two-temperature operation may utilize an evaporator pressureregulator.■ Relief valves prevent high pressures from occurring in thesystem.

■ Electrical controls stop, start, or modulate electron flow forthe control of motors and fluid flow.■ When energized, the solenoid valve, a valve with a magneticcoil, will open or close a valve to control fluid flow.■ Pressure switches stop and start system components.■ The low-pressure switch can be used for low-charge protectionand as a thermostat.■ The high-pressure switch protects the system against highoperating pressures. This control can be either manual orautomatic reset.■ The low-ambient control (switch) maintains the correct operatinghead pressures on air-cooled equipment in both mildand cold weather by cycling the condenser fan.■ The oil safety switch ensures that the correct oil pressureis available 90 sec after start-up on larger compressors(normally above 5 hp).■ Defrost with internal heat can be accomplished with hot gasfrom the compressor.■ Defrost with external heat is normally done with electricheaters in the vicinity of the evaporator. The compressormust be stopped during this defrost.■ Refrigeration accessories normally do not automaticallychange the flow of refrigerant but enhance the operation ofthe system.■ Refrigeration system accessories can be service valves, filterdriers, sight glasses, refrigerant distributors, heat exchangers,storage tanks, oil separators, vibration eliminators, or pressuretaps.■ No system must have all of these components, but all systemswill have some of them.■ Crankcase heat is required for many refrigeration systems,especially R-22 refrigerant systems because of refrigerantmigration during downtime. Damage can occur to the compressorif it is started while excessive refrigerant is in thecrankcase.

SUMMARY■ Product dehydration can be a factor in the choice ofequipment.■ With package or self-contained equipment, the condenserrejects the heat back into the store when the equipment islocated inside.■ The condensing unit in packaged equipment is normally ontop or underneath the fixture.■ All fixtures have condensate that must be drained away orevaporated.■ Fixtures may also be piped to a common equipment room witheither individual compressors or single-compressor units.■ When a single large compressor is used, capacity control isdesirable.■ Load matching can be accomplished with parallel compressorsystems. These compressors are manifolded together with acommon suction and discharge line. They share one receiver.■ Apressure transducer on the common suction line signals thecontroller on the parallel compressor rack for capacity steps.■ Acomplicated oil system is used on parallel compressor systemsto ensure the proper oil level in each compressor’scrankcase.■ Parallel compressor systems often use satellite or booster

compressors, which are usually the largest compressors onthe racks.■ Secondary-fluid systems circulate an antifreeze solution tothe refrigerated cases and offer many advantages over a conventionalrefrigeration system.■ Pressurized liquid systems offer a different way to subcoolliquid refrigerant. This helps in overcoming any pressuredrops in the liquid line to prevent premature flashing of theliquid before it enters the metering device.■ Unitary, stand-alone refrigeration modules offer many advantagesas compared with a conventional supermarket refrigerationsystem with an equipment room.■ Capacity control is accomplished by cycling compressors onthe multiple-compressor racks.■ Several evaporators may be piped together to a common suctionline.■ The liquid lines are manifolded together after the liquidleaves the receiver.■ Each fixture has its own expansion valve.■ There must be a defrost cycle on both medium- and lowtemperaturefixtures.■ Heat must be added to the coil for defrost in low-temperaturerefrigeration systems.■ Common discharge lines concentrate the heat that was absorbedinto the system.■ This heat can be used to heat the store or heat water withheat-recovery devices.■ Heaters are used around the doors to keep the cabinet aroundthe doors above the dew point temperature of the room.■ These heaters, called mullion heaters, normally produceelectric resistance heat that is sometimes thermostaticallycontrolled.■ Humidity, usually in the summer, leaves the store by twomeans: the refrigeration equipment and the air-conditioningequipment.■ It is less expensive to remove humidity with the airconditioningequipment than with the refrigeration equipmentdefrost cycle.■ Drain heaters normally produce electric resistance heat andmay have thermostats to keep them from operating whenthey are not needed.■ Some coolers have remote condensing units, and some havewall-hung or roof-mount package equipment.■ Some of the remote units are field piped, and some are pipedwith quick-connect tubing.■ The refrigeration vending machine systems consist of themoney receiving-and-changing mechanism, the food handlingsection (often called the conveyor), and the refrigerationsystem.■ Defrosted condensate flows to a sealed drain to be evaporatedusing moving air or the hot gas line.■ Vending refrigeration uses air-cooled condensers that havefractional horsepower compressors and often forced-draftevaporators.■ Water coolers dispense cold water, are self-contained, anduse a fractional horsepower compressor and an air-cooledcondenser. The evaporator is a container with the evaporatorpiping wrapped around it.

■ Water coolers are package refrigeration machines that maybe either free standing or hung on the wall. A drain must beconnected back to the building drain system.■ Refrigerated air driers are refrigeration systems that are usedto dehydrate air that is compressed with an air compressor.■ Refrigerated air driers typically operate all of the time,whether there is a load or not. They provide cooling to about35°F.■ The typical refrigerated air drier uses a hermetic compressorand either an air- or water-cooled condenser.■ SAFETY PRECAUTION: There are many applications for refrigeration.There is no substitute for knowing the manufacturer’sintent. Do not improvise without this knowledge.

SUMMARY■ Most ice flakers are critically charged refrigeration systemsthat come in a split or a self-contained unit.■ Ice flake machines use an auger turning inside a floodedcylinder to scrape ice off the sides of the cylinder.■ The auger has cutting surfaces called flights that do the icecutting.■ Ice flake machines can be retrofitted to parallel refrigerationsystems in a supermarket.■ When water is frozen in the evaporator or freezing cylinder,minerals from the water are left behind and often become attachedto the interior cylinder walls.■ An ice machine cleaner will dissolve many minerals from thefreezing section of an ice flake machine.■ Mineral buildup on the freezing cylinder of an operating iceflake machine will cause a sound like two pieces of Styrofoambeing rubbed together.■ Ice flake machines usually have a gear reduction drive,which reduces the auger’s drive motor speed.■ Mineral buildup on a freezing cylinder of an ice flakemachine will cause auger motor and auger bearings to bestressed. Gears will also be stressed.■ The gear motor assembly is more prone to fail than any otherpart in the ice flake machine because of the pressures andstresses put on it.■ Worn bearings on the auger will cause the auger to wobble andrub against the freezing cylinder walls. This often causes scrapemarks on the cylinder walls and metal shavings in the ice.■ A dual float switch and a water control valve usually controlthe amount of water coming into an ice flaker’s water reservoirand also provide for ice machine shutdown in case oflow water.■ A water flush cycle is a way to control unwanted mineralbuildup in the water reservoir. A mechanical timer or amicroprocessor can initiate these cycles.■ Ice bin controls are designed to terminate the operation of theice machine when the bin is full of ice.■ Ice production depends on the ice machine’s water inlet temperatureand the temperature around the ice machine. As thewater temperature or air temperature surrounding the icemachine rises, ice production drops.■ Some ice flake machines provide a means for the servicetechnician or owner to adjust the size or shape of the iceflakes. Rotating the ice cutter or changing the extrusion headare ways to accomplish this.

■ Some ice machines make flat ice on a flat evaporator to a predeterminedthickness. The flat ice sheet then falls or slidesonto a grid of cutting wires. The wires have a low voltage toprovide heat to cut the ice.■ Making crescent-shaped ice involves running water over anevaporator plate in which copper evaporator tubing is solderedonto the plates at regular intervals. The coldest pointson the evaporator are where the copper coil contacts theevaporator plate. Ice starts to form here first.■ During a hot gas harvest, the cubes slide down the evaporatorplate by gravity. Dimples in the evaporator plate willbreak the capillary attraction between the plate and thecrescent-shaped cube. Ice then falls in a bin for storage.■ Making cell-type ice cubes involves having a vertical evaporatorplate with water flowing over the individual cells by awater pump. A serpentine evaporator coil is soldered to theback of the plate. Ice gradually forms in the cells and soonbridges with the neighboring cell.■ Too slow a water flow will freeze minerals with the ice. Arestrictor in the water line regulates the water flow rate.■ Once a certain bridge thickness is reached, the water filmon the ice will contact an adjustable ice thickness probe. Ahot gas harvest is then initiated.■ A hot gas solenoid is energized in the discharge line. Thecompressor keeps running and pumps superheated gasthrough the evaporator.■ A hot gas defrost loosens the cubes from the evaporatorplate. Either by gravity or by a pushrod, the ice comes off theevaporator plate and falls into a storage bin.■ Weep holes between the cells on the evaporator allow airentering from the edges of the ice sheet to travel along theentire ice slab. This relieves the attractive suction forcesbetween the evaporator plate and the ice sheet.■ Cylindrical ice is made inside a tube-within-a-tube evaporator.As water flows through the center tube, it freezes on theoutside walls of the tubes. Defrost lets the ice shoot out theend of the tube as a long cylinder.■ Many different control schemes and controls from differentice machine manufacturers are used for water sump levels,ice thickness, harvest initiation, defrost termination, and icestorage bin controls.■ During hot gas defrost or harvest, liquid floodback may occurto the compressor. To combat this, a thermistor is placedon the discharge line of the compressor to sense the dischargetemperature. A cold discharge line during a harvestperiod usually means liquid floodback to the compressor.■ Hot gas valves are often cycled by a microprocessor while inharvest in response to the discharge temperature to controlliquid floodback.■ Microprocessors are often the main controller on modern icemachines. They have stored programs or algorithms withinthem. This is actually a stored sequence of events in theirmemories.■ Microprocessors have input and output terminals where theyreceive and transmit information, respectively. Inputs andoutputs can be either digital devices, like switches or analogdevices, like thermistors.■ A service technician should know the microprocessor’s sequence

of events and how to input/output troubleshoot them.Service manuals and the Internet are often used to gainknowledge of a certain manufacturer’s microprocessorsequence of events.■ Many microprocessors have self-diagnostics to assist theservice technician in systematic troubleshooting.■ Microprocessors also have error codes, which can be displayedto assist the service technician in troubleshooting.■ Many microprocessors can record the ice machine’s history orsummary of past operations. This memory can then be recalledby simply pushing buttons. Information that has been gatheredover a long period of time, like the number of harvests, errorcodes stored, and average cycle times, can be recalled.■ For air-cooled ice machines, ice production depends mainlyon entering-water temperature and the temperature of the airentering the condenser.■ For air-cooled ice machines, suction pressure, head pressure,electrical consumption, and other system performance factorsmainly depend on entering-water temperature and thetemperature of the air entering the condenser.■ Ice quality depends on the quality of the water entering theice machine. Good water quality will produce a crystal-clearhard cube with good cooling capacity. Poor water quality canproduce soft, cloudy ice with less cooling capacity.■ Water can contain many different minerals in various levels.Water filtration and treatment is a science in itself, but the servicetechnician needs to know the basics of water quality toservice ice makers. Important terms to know are filtration, treatment,sediment, flow rate, scale, scale inhibitor, water softener,reverse osmosis, iron, total dissolved solids, turbidity, pH,acidic water, alkaline, chlorine, chloramines, and hardness.■ Ice quality is measured in percent of hardness. Hardness is ameasurement that represents the thermal cooling capacity ofthe ice. The higher the percent hardness, the more coolingcapacity the ice possesses.■ The cleaner the ice machine and the purer the water, theharder the ice will be.■ Preventive maintenance is the action of regularly scheduledmaintenance performed on an ice machine. It includes inspecting,cleaning, sanitizing, and servicing the ice machineand external water filtration/treatment system.■ Cleaning an ice machine with an acid-based cleaner simplyremoves scale from the mineral content in the water.■ A sanitizing fluid that is approved for commercial ice machineskills viruses, bacteria, and protozoa.■ If cleaning and sanitizing are done on a schedule that is appropriatefor the local water conditions, the ice machine willhave a longer and more productive life dispensing quality ice.■ Water treatment programs are designed for local areas to helpwith certain water conditions. Water conditions can be brokendown into suspended solids, dissolved minerals, andchemicals.■ A common type of water treatment is a triple-action filtersystem that can filter out suspended solids, fight against scaleformation by adding chemicals, and improve the taste, odor,and color of the water with carbon filters.

SUMMARY■ Transport refrigeration is the process of transporting various

refrigerated products by truck, rail, air, or water.■ Vegetables shipped from California to New York will needrefrigeration while crossing the hot desert and may even needheat when traveling in the cold northern states.■ Some products are shipped at medium temperatures andsome at low temperatures in the frozen state.■ Dry ice, made from compressed carbon dioxide (CO2), maybe used to refrigerate loads. It changes state from a solid to avapor without going through the liquid state, called sublimation,at _109°F. It is particularly good for low-temperatureloads.■ Liquid nitrogen or CO2 may also be used for refrigeration.The liquid is stored in low-pressure cylinders with a relief valve system that maintains the cylinder pressure at about25 psig by relieving excess pressure from the cylinder.Nitrogen evaporates at _320°F and CO2 at _109°F.■ These systems are simple, with only a thermostat controllinga solenoid valve. A distribution system distributes the coldnitrogen vapor.■ SAFETY PRECAUTION: Nitrogen and CO2 must be handledwith care because they are so cold. They can freeze fleshimmediately on contact. Be sure to wear protective clothing,gloves, and goggles when working with either ofthese systems. Both of these vapors also displace oxygenso the system cannot be operating while people are in therefrigerated space. Special controls shut the system off ifthe door is opened to the refrigerated space.■ Trucks are often equipped with refrigerated plates that containa solution called a “eutectic solution” that goes througha phase change when cooled and warmed. The solution istypically a brine solution of either sodium chloride (tablesalt) or calcium chloride.■ These brine solutions are corrosive to ferrous metals.■ The brine solution does not actually turn solid; it turns tocrystals when frozen and the crystals turn to liquid whenwarmed.■ Trucks may also be refrigerated using mechanical refrigerationlocated on the truck.■ When at the dock, the compressor may be plugged into apower supply.■ Larger trucks use either nose-mount or under-belly refrigerationunits.■ The evaporator and fan are located in the front of the truck ona typical unit.■ Truck systems are not designed to have the capacity to refrigeratea load that is not down to temperature. They are meantto hold the load temperature while in transit.■ Truck bodies are insulated and the doors have gaskets toprevent infiltration.■ Two-speed engines and compressors that unload are used forcapacity control.■ Extra-low-temperature refrigerated applications at temperaturesbelow _10°F often use the compression cycle by usingeither two-stage compressors or cascade refrigerationsystems.■ Cascade refrigeration systems use more than one stage ofrefrigeration to reach very low temperatures.■ Fresh food that is frozen quickly retains its fresh color and

taste. The quicker the food is frozen, the better these qualitieswill be maintained.■ When meats are frozen slowly, the ice crystals form slowlyand puncture the cell walls of the meat.■ Food may be frozen quickly by dipping it in a cold solution,such as brine (salt water), or it may be frozen quickly by usingblast freezers, very cold air blowing directly on the food.The cold air and the velocity help to remove heat from thefood quickly.■ Conventional refrigeration systems may be used for blastfreezing.■ Ship refrigeration may have several applications, frommedium temperature to low temperature.■ A fish processing ship must have the capability of quickfreezing and holding the fish after they are processed.■ Refrigerated cargo ships may have large refrigerated holdswhere plate-type or forced-draft evaporators are used tomaintain the temperature.■ The condensers for ship refrigeration usually use sea waterand are made of cupronickel.■ Another method for shipping refrigerated cargo is to use self-containedair-cooled refrigeration on containerized freight.■ Ships must also have refrigeration for the ship’s stores.■ Many products are shipped by air to speed them to market(e.g., flowers). They are typically kept cool using ice or dry ice.

SUMMARY■ The technician should know how the equipment shouldsound, where it should be cool, and where it should be warm.■ All evaporators that cool air have a relationship with the airthey are cooling. The coil will generally boil the refrigerantbetween 10°F and 20°F colder than the air entering theevaporator.■ High-temperature evaporators normally operate betweenliquid-refrigerant boiling temperatures of 25°F and 40°F.■ Medium-temperature evaporators normally operate betweenliquid-refrigerant boiling temperatures of 10°F and 25°F.■ Low-temperature food storage systems normally operatebetween liquid-refrigerant boiling temperatures of _15°Fdown to about _49°F.■ There is a relationship between entering air and condensingrefrigerant. Usually refrigerant should not condense at morethan 30°F higher than the entering air, and high-efficiencycondensers at no more than 25°F higher.■ The automatic expansion valve maintains a constant lowsidepressure. For this reason the low-side pressure does notgo down during low charge operation as with a capillary tubeand a TXV.■ An overcharge of refrigerant always causes an increase inhead pressure.■ An increase in head pressure causes an increase in suctionpressure when the TXV or the capillary tube is the meteringdevice.■ An increase in head pressure causes more refrigerant to flowthrough a capillary tube. Liquid refrigerant may flood intothe compressor with an overcharge.■ The automatic expansion valve responds in reverse to loadchanges. When the load is increased, the valve throttles back

and will slightly starve the evaporator. When the load is decreasedexcessively, the valve is subject to overfeed the coiland may allow small amounts of liquid refrigerant to enterthe compressor.■ When an inefficient evaporator is encountered, the refrigerantboiling temperature will be too low for the entering-airtemperature.■ When an inefficient condenser is encountered, the condensingrefrigerant temperature will be too high for the heatrejection medium.■ The best check for an inefficient compressor is to see if it willpump to capacity.■ Design load conditions can almost always be duplicated bybuilding the head pressure up and duplicating the designsuction pressure.

SUMMARY■ Electric heat is a convenient way to heat individual roomsand small spaces.■ Central electric heating systems are usually less expensive toinstall and maintain than other types.■ Operational costs may be higher than with other types offuels.■ The low-voltage thermostat, sequencer, and relays are controlmechanisms used in central electric forced-air systems.■ The sequencer is used to activate the heating elements instages. This avoids putting heavy kilowatt loads in service atone time. If this were done, it could cause fluctuations inpower, resulting in voltage drop, flickering lights, and otherdisturbances.■ Sequencers have bimetal strips with 24-V heaters. Theseheaters cause the bimetal strip to bend, closing contacts andactivating the high-voltage heating elements.■ The fan in a central system must operate while the heating elementsare on. The systems must be wired to ensure that thisoccurs.■ Systems are protected with limit switches and fusible links(temperature controlled).■ Preventive maintenance inspections should be made periodicallyon electric heating units and systems.

SUMMARY■ Forced-hot-air furnaces are normally classified as upflow,downflow (counterflow), horizontal, low-boy, or multipoise.■ Multipoise furnaces can be installed in any position, whichadds versatility. Multiple safety controls like bimetallicflame rollout or overtemperature limits must be designedinto the furnace for safety.■ Auxiliary limit switches, which sense room return air temperature,interrupt the burner operation when the temperaturegets too hot.■ Vent limit or draft safeguard switches are normally closedswitches and are usually mounted on the draft hood or nearthe exhaust vent pipe exit. They monitor the draft hood temperatureand open when there is any spillage of flue gas.■ Furnace components consist of the cabinet, gas valve, manifold,pilot, burners, heat exchangers, blower, electrical components,and venting system.■ Gas fuels are natural gas, manufactured gas (used in few

applications), and LP gas (propane, butane, or a mixture ofthe two).■ Inches of water column is the term used when determining orsetting gas fuel pressures.■ A water manometer or digital manometer measures gas pressurein inches of water column.■ For combustion to occur there must be fuel, oxygen, andheat. The fuel is the gas, the oxygen comes from the air, andthe heat comes from the pilot flame or other igniter.■ Gas burners use primary and secondary air. Excess air is alwayssupplied to ensure as complete combustion as possible.■ Gas valves control the gas flowing to the burners. The valvesare controlled automatically and allow gas to flow only whenthe pilot is lit or when the ignition device is operable.■ Some common gas valves are classified as solenoid, diaphragm,or heat motor valves.■ A servo pressure regulator is an outlet or working pressureregulator. It monitors gas outlet pressure when gas flow ratesand inlet pressures vary widely.■ A redundant gas valve has two or three valve operators physicallyin series with one another but wired in parallel.■ Ignition at the main burners is caused by heat from the pilotor from an electric spark. There are standing pilots that burncontinuously, and intermittent pilots that are ignited by aspark when the thermostat calls for heat. There is also adirect-spark or direct burner ignition, in which the spark orhot surface igniter ignites the gas at the burners.■ The thermocouple, the bimetal, and the liquid-filled remotebulb are three types of safety devices (flame-proving devices)to ensure that gas does not flow unless the pilot is lit.■ The manifold is a pipe through which the gas flows to theburners and on which the burners are mounted.■ The orifice is a precisely sized hole in a spud through whichthe gas flows from the manifold to the burners.■ The burners have holes or various designs of slots throughwhich the gas flows. The gas burns immediately on the outsideof the burners at the top or end depending on the type.■ Inshot burners are usually made of aluminized steel and havecrossover porting for good flame retention, proper flame carryoverto each main burner, and excellent flame stability.■ Modern gas furnaces use either induced- or forced-draftsystems. Induced-draft systems have a combustion blowermotor located on the outlet of the heat exchanger. They pullor suck combustion gases through the heat exchanger, usuallycausing a slight negative pressure in the heat exchangeritself.■ Forced-draft systems have a combustion blower motor on theinlet of the heat exchanger. They push or blow combustiongases through the heat exchanger and cause a positive pressurein the heat exchanger.■ The gas burns in an opening in some heat exchangers. Airpassing over the heat exchanger is heated and circulated tothe conditioned space.■ A blower circulates this heated air. The blower is turned onand off by a fan switch, which is controlled either by time orby temperature.■ Modern heat exchangers come in many sizes, shapes, andmaterials. Many are L-shaped and S-shaped and made of aluminized

steel. There is actually a serpentine path for combustiongases to travel. Serpentine heat exchangers use inshotburners instead of ribbon or slotted-port burners.■ Modern condensing furnaces may have two or even threeheat exchangers. The last heat exchanger is usually made ofstainless steel or aluminum to resist corrosion. It is designedto intentionally handle condensate and eventually drain itaway from the furnace.■ Many modern gas furnaces use electronic modules or integratedfurnace controllers (IFCs) to control operations.These controllers often have dual in-line pair (DIP) switches,which can be switched to reprogram the furnace to make itmore versatile.■ The limit switch is a safety device. If the fan does not operateor if the furnace overheats for another reason, the limitswitch causes the gas valve to close.■ High-limit switches come in a variety of styles such asbimetallic snap action, helical bimetal, or liquid filled. Theycome as either manual or automatic resettable.■ In a flame rectification system, the pilot flame, or mainflame, can conduct electricity because it contains ionizedcombustion gases that are made up of positively and negativelycharged particles. The flame is located between twoelectrodes of different sizes. The electrodes are fed with analternating current from the furnace’s electronic module orcontroller. Current will flow in one direction more than theother because of the different size electrodes. The flame actsas a switch. When the flame is present, the switch is closedand will conduct electricity.■ Flame rectification systems can be classified as eithersingle rod (local sensing) or dual rod (remote sensing).Single-rod systems consist of an igniter and a sensor allin one rod. Dual-rod systems use a separate igniter andflame-sensing rod.■ A direct-vented high-efficiency gas furnace has a sealedcombustion chamber. This means that the combustion airis brought in from the outside through an air pipe, which isusually made of PVC plastics. A non-direct-vented highefficiencygas furnace uses indoor air for combustion.■ A positive pressure system can be vertically or sidewallvented. Its flue pipe pressure is positive the entire distance toits terminal end.■ The dew point temperature is the temperature at which thecondensation process begins in a condensing furnace. TheDPT varies depending on the composition of the flue gas andthe amount of excess air. As excess air decreases, the DPTincreases.■ Excess air consists of combustion air and dilution air. Combustionair is primary air and/or secondary air. Primary airenters the burner before combustion takes place. Secondaryair happens after combustion and supports combustion.■ Dilution air is excess air after combustion and usually entersat the end of the heat exchanger.■ Furnace efficiency ratings are determined by the amount ofheat that is transferred to the heated medium. Factors that determinethe efficiency of a furnace are the type of draft, theamount of excess air, the temperature difference of the air orwater entering versus leaving the heating medium side of the

heat exchanger, and the flue stack temperature.■ Electronic ignition modules come in 100% shutoff, non-100% shutoff, continuous retry with 100% shutoff, and manyother custom control schemes that are manufacturer dependent.The combustion blower can prepurge, interpurge, orpostpurge the heat exchanger depending on the modules’control scheme.■ Twinning involves the operation of two side-by-side furnacesconnected by a common ducting system. Twinning is oftenused when the required heating capacity is greater than thelargest-capacity furnace manufactured. It is also used whenthe airflow of one furnace, for air-conditioning purposes, isgreater than a single furnace can provide.■ Modern two-stage gas furnaces use a two-stage gas valve anda two-speed combustion blower motor with two pressureswitches to prove the draft.■ Modern modulating gas furnaces follow the heat loss of astructure. They use a modulating gas valve instead of astaged valve. They also come with variable-speed warm airblowers to vary the speed and amount of warm air. Variableoutput thermostats that send a proportional signal instead ofan on-off signal to the furnace controller often control modulatingfurnaces.■ One of the first steps in systematically troubleshooting a furnacewith an integrated furnace controller is to obtain theelectrical diagram of the furnace and sequence of operationof the IFC.■ SAFETY PRECAUTION: Venting systems must provide asafe and effective means of moving the flue gases to theoutside atmosphere. Flue gases are mixed with other airthrough the draft hood. Venting may be by natural draft orby forced draft. Flue gases are corrosive.■ Gas piping should be kept simple with as few turns and fittingsas possible. It is important to use the correct pipe size.■ SAFETY PRECAUTION: All piping systems should betested carefully for leaks.■ The combustion efficiency of furnaces should be checkedand adjustments made when needed.■ Preventive maintenance calls should be made periodically ongas furnaces.

SUMMARY■ No. 2 grade fuel oil is most commonly used in heating residencesand light commercial buildings.■ Fuel oil is composed primarily of hydrogen and carbon inchemical combination.■ Gun-type oil burner parts are the burner motor, blower or fanwheel, pump, nozzle, air tube, electrodes, ignition system,and primary controls.■ The pump can be single or dual stage.■ Air is blown through the air tube into the combustion chamberand mixed with the atomized fuel oil.■ The ignition system provides the high voltage, producing thespark across the electrodes.■ Ignition can be interrupted or intermittent.■ Interrupted ignition systems provide a spark only at the beginningof the cycle.■ Intermittent ignition provides a continuous spark.

■ Fuel storage and supply systems can be one-pipe or two-pipedesign.■ An auxiliary or booster supply system must be used wherethe burner is more than 15 ft above the storage tank.■ The atomized oil and air mixture is ignited in the combustionchamber.■ The heat exchanger takes heat caused by the combustion andtransfers it to the air that is circulated to heat the building.■ The performance of the pump can be checked with a vacuumgage and a pressure gage.■ One-pipe systems must be bled before the burner is startedfor the first time or whenever the fuel supply lines have beenopened.■ To convert a pump from a one-pipe to a two-pipe system, inserta bypass plug in the return or inlet port.■ Nozzles should not be cleaned or unplugged. They should bereplaced.■ Electrodes should be clean, connections should all be secure,and the spark gap should be adjusted accurately.■ Combustion efficiency tests should be made when servicingoil burners, and corrective action taken to obtain maximumefficiency.■ Preventive maintenance procedures should be performedannually.

SUMMARY■ Hydronic heating systems use hot water or steam to carryheat to the areas to be heated.■ A boiler is an appliance that heats water. In gas and oil systemsthe part of the boiler containing the water is constructedin sections or tubes.■ Cast-iron and steel boilers are classified as high-massboilers.■ Copper-tube boilers are classified as low-mass boilers.■ A limit control is used to shut the heat source off if the watertemperature gets too high.■ A low-water cut-off shuts down the heat source if the waterlevel gets too low.■ A pressure relief valve is required to discharge water when excessivepressure is created by expansion due to overheating.■ An air cushion tank or expansion tank is necessary to providespace for trapped air and to allow for expansion of the heatedwater.■ Zone control valves are thermostatically operated and controlthe flow of hot water into individual zones.■ A centrifugal pump circulates the water through the system.■ The “point of no pressure change” is the point in a hydronicsystem where the water pressure does not change; it islocated at the inlet of the expansion tank.■ Finned-tube baseboard terminal units are commonly used inresidential hydronic heating systems.■ A balancing valve is used to equalize the flow rate in differentheating circuits.■ Outdoor reset control is used to change the temperature ofthe boiler water in response to changes in the outside ambienttemperature.■ The series loop system is the most economical hydronic systemto install but does not allow for individual terminal-unittemperature control.

■ One-pipe systems and two-pipe reverse-return piping systemsare most commonly used in residential and light commercialinstallations.■ A one-pipe system requires a specially designed tee to divertsome water to the baseboard unit while allowing the rest toflow through the main pipe.■ Primary–secondary pumping allows for multiple-temperatureoperation for multizone systems.■ Mixing valves are used to achieve different water temperaturesat different points in a hydronic system.■ Radiant heating systems use lower water temperatures toprovide heating.■ Popular radiant heating system installation types include slabon grade, thin slab, and dry/staple-up.■ Tankless domestic hot water heaters are commonly used withhot water heating systems. The water is contained within acoil and heated by the boiler.■ Hydronic systems should be serviced with proper preventivemaintenance procedures annually.

SUMMARY■ Many modern homes and office buildings are being designedand constructed to keep the outside air out in order to maximizeheating and cooling efficiencies. This may result in theaccumulation of air pollutants inside.■ Eliminating the source of indoor pollution should be the firststep in improving indoor air quality.■ Mold growth indoors has become a major problem.■ Indoor air quality can be improved through the use of ventilation,which removes some air pollutants and dilutes thoseremaining.■ Air cleaning through the use of filtering, absorption, andadsorption is another means for improving indoor airquality.■ Ducts may be cleaned if there is significant evidence that itshould be done.■ In cool or cold weather, humidifiers may be needed for comfortand to protect furniture and other household materials.

SUMMARY■ Comfort describes the delicate balance of feeling in relationshipto our surroundings.■ The body stores energy, wastes it, consumes it in work, orgives the heat off to the surroundings.■ For the body to be comfortable, it has to be warmer thanthe surroundings, so it can give up excess heat to thesurroundings.■ Air contains 78% nitrogen, 21% oxygen, 1% other gases, andsuspended water vapor.■ The specific volume of air is the reciprocal of the density:1_0.075 _ 13.33 ft3/lb.■ The moisture content of air can vary the transfer of heat fromthe human body; therefore, different temperatures and moisturecontent can give the same relative comfort level.■ Dry-bulb temperature is registered with a regular thermometer.■ Wet-bulb temperature is registered with a thermometer thathas a wet wick. The wet-bulb thermometer lead gets colderthan the dry-bulb thermometer lead because the moisture onthe wick evaporates.

■ The difference between the wet-bulb reading and the drybulbreading is the wet-bulb depression. It can be used todetermine the relative humidity of a conditioned space.■ Water vapor in the air creates its own vapor pressure.■ The wet-bulb reading on a psychrometric chart shows thetotal heat content of a pound of air.■ When the cubic feet of air per minute is known, the wet-bulbreading in and out of an air exchanger can give the total heatbeing exchanged. This can be used for field calculating thecapacity of a unit.

SUMMARY■ Evaporative cooling may be used in areas where the temperatureis high and the humidity is low.■ Refrigerated air conditioning cools the air and removesmoisture.■ Refrigerated air conditioning is used in hot temperatureswith high or low humidity.■ Evaporators are made in three types: the A coil, slant coil,and H coil.■ Air-conditioning evaporators operate at about 40°F andremove sensible heat and latent heat.■ Removal of sensible heat lowers the air temperature; removalof latent heat removes moisture.■ The compressor is the positive displacement pump that pumpsthe heat-laden vapor from the evaporator to the condenser.■ Condensers are located outside to reject the heat to theoutside.■ High efficiency in a condenser is achieved by increasing thecondenser surface area. Two-speed fans may be used, onespeed for mild weather and the other for hot weather.■ Package air conditioners are installed through the roof orthrough the wall at the end of the structure, wherever the ductcan be fastened.■ The package unit is charged at the factory and is factory assembled.Under similar conditions, it is more efficient thanthe split system.

SUMMARY■ Air is passed through conditioning equipment and then circulatedinto the room to condition it.■ Infiltration is air leaking into a structure.■ Ventilation is air being induced into the conditioning equipmentand conditioned before it is allowed to enter the conditionedspace.■ The duct system distributes air to the conditioned space. Itconsists of the blower (or fan), the supply duct, and the returnduct.■ The blower or fan uses energy to move the air.■ The propeller type is used to move a lot of air against a smallpressure. It can make noise.■ The centrifugal type is used to move large amounts of air inductwork, which offers resistance to the movement of air.■ A fan is not a positive-displacement device.■ Small centrifugal fans use energy in proportion to the amountof air they move.■ Duct systems, both supply and return, are large pipes or tunnelsthat the air flows through.■ 1 in. WC is the amount of pressure needed to raise a column

of water 1 in.■ The atmospheric pressure of 14.696 psia will support a columnof water 34 ft high.■ 1 psi will support a column of water 27.7 in. or 2.31 fthigh.■ Static pressure is the pressure pushing outward on theduct.■ Velocity pressure is moving pressure created by the velocityof the air in the duct.■ Total pressure is the velocity pressure plus the staticpressure.■ The pitot tube is a probe device used to measure the airpressures.■ Air velocity (fpm) in a duct can be multiplied by the crosssectionalarea (ft2) of the duct to obtain the amount of airpassing that particular point in cubic feet per minute.■ Typical supply duct systems used are plenum, extendedplenum, reducing plenum, and perimeter loop.■ Branch ducts should always have balancing dampers to balancethe air to the individual areas.■ Zoning allows a single air-conditioning system to provide individualroom temperature control.■ When a system is zoned, each zone has its own zone damperand space thermostat.■ Zoned systems can provide simultaneous heating and coolingto different zones.■ When the air is distributed in the conditioned space, it iscommon practice to distribute the air on the outside wall tocancel the load.■ The amount of throw tells how far the air from a diffuser willreach into the conditioned space.■ Each foot of duct, supply or return, has a friction loss that canbe plotted on a friction chart for round duct.■ Round duct sizes can be converted to square or rectangularequivalents for sizing and friction readings.

SUMMARY■ Duct systems are normally constructed of square, rectangular,or round metal; ductboard; or flexible material.■ Square and rectangular metal duct systems are assembledwith S fasteners and drive clips.■ The first fitting in a duct system may be a vibration eliminatorto keep any fan noise or vibration from being transmittedinto the duct.■ Insulation may be applied to the inside or outside of anymetal duct system that may exchange heat with the ambient.■ When the duct is insulated on the outside, a vapor barriermust be used to keep moisture from forming on the duct surfaceif the duct surface is below the dew point temperature ofthe ambient.■ Flexible duct is a flexible liner that may have a cover of fiberglassthat is held in place with vinyl or reinforced foil.■ The electrical installation includes choosing the correct enclosures,wire sizes, and fuses or breakers.■ The electrical contractor will normally install the linevoltagewiring, and the air-conditioning contractor will usuallyinstall the low-voltage control wiring. Local codesshould be consulted before any wiring is done.■ The low-voltage control wiring is normally color coded.

■ Air-conditioning equipment is manufactured in package systemsand split systems.■ Air-to-air package equipment installation consists of placingthe unit on a foundation, connecting the ductwork, and connectingthe electrical service and control wiring.■ The duct connections in package equipment may be madethrough a roof or through a wall at the end of a structure.■ Roof installations have waterproof roof curbs and factorymadeduct systems.■ Isolation pads or springs placed under the equipment preventequipment noise from traveling into the structure.■ Two refrigerant lines connect the evaporator and the condensingunit; the large line is the insulated suction line, andthe small line is the liquid line.■ The air handler and condenser should be installed so thatthey are accessible for service.■ A condensate drain provision must be made for theevaporator.■ A secondary drain pan should be provided if the evaporatoris located above the conditioned space.■ The condensing unit should not be located where its noisewill be bothersome.■ Line sets come in standard lengths of 10, 20, 30, 40, and50 ft. The system charge is normally for 30 ft when the wholecharge is stored in the condensing unit.■ Line sets may be altered in length. The refrigerant chargemust be adjusted when the lines are altered.■ The start-up procedure for the equipment is in the manufacturer’sliterature. Before start-up, check the electrical connections,the fans, the airflow, and the refrigerant charge.

SUMMARY■ The control of air-conditioning equipment consists ofcontrolling the various components in order to start and stopthem in the correct sequence to maintain space temperaturefor comfort.■ The three main components controlled are the indoor fan, thecompressor, and the outdoor fan.■ The control circuit uses low voltage (24 V) for safety.■ Low voltage is obtained from high voltage by a transformerlocated in the condensing unit or in the air handler.■ Some electronic thermostats use a thermistor as the sensingdevice and may incorporate other features, such as temperaturesetback, for night and day.■ Air-cooled equipment is used more widely today than watercooledequipment.■ Controls are either operating controls or safety controls.■ Some controls, such as contactors and electronic thermostats,have more than one circuit.■ The compressor overload protectors are used to keep thecompressor from drawing too much current and overworking.■ The motor-winding thermostat shuts off the compressorwhen the compressor motor winding gets too hot.■ The compressor internal relief valve vents high-pressuregas from the high-pressure side to the low-pressure side ofthe compressor internally. It can be used as a high-pressureindicator by directing this high-pressure, high-temperaturegas onto the winding thermostat.■ Modern equipment may have only a few controls and

components. It is common for the unit to have a singlepolecontactor and a run capacitor as the only visiblecomponents.■ Electronic circuit boards are furnished with some equipment.The circuit boards may include short-cycle protection, aswell as low- and high-voltage protection.

SUMMARY■ The inside conditions that vary the load on the system are thespace temperature and humidity.■ When the discharge pressure rises, the system capacitydecreases.■ High-efficiency systems often use larger or oversizedevaporators, and the refrigerant will boil at a temperatureof about 45°F at typical operating conditions. This is a temperaturedifference of 30°F compared with the return air.■ High-efficiency equipment has a lower operatinghead pressure than standard-efficiency equipment partlybecause the condenser is larger. It has a different relationshipto the outside ambient temperature, normally20°F to 25°F.■ The first thing that the technician needs to know for electricaltroubleshooting is what the operating voltage for the unitis supposed to be.■ Equipment manufacturers require that operating voltages of_10% of the rated voltage of the equipment be maintained.■ The unit may have the compressor’s RLA printed on it. Itshould not be exceeded.■ Some manufacturers are now using two-speed motors andvariable-speed motors for variable capacity.

SUMMARY■ The superheat for an operating evaporator coil is used toprove coil performance.■ Standard air-conditioning conditions for rating equipmentare 80°F return air with a humidity of 50% when the outsidetemperature is 95°F.■ The typical customer operates the equipment at 75°F returnair with a humidity of 50%. This is the condition that the normalpressures and temperatures in this unit are based on.■ Ahigh-efficiency evaporator normally has a boiling temperatureof 45°F.■ Gages fastened to the high side of the system are used tocheck the head pressure. The head pressure is a result of therefrigerant condensing temperature.■ The condensing refrigerant temperature has a relationship tothe medium to which it is giving up heat.■ A standard-efficiency unit normally condenses the refrigerantat no more than 30°F higher than the air to which the heatis rejected.■ A high-efficiency condensing unit normally condenses therefrigerant at a temperature as low as 20°F warmer than theair used as a condensing medium.■ Approach temperature, or temperature split, are terms used todescribe the temperature difference between two differentheat exchange mediums, for example, the return air temperatureand coil boiling temperature of a refrigerant evaporator.■ Temperature difference is a term used to describe the differencebetween the inlet and outlet temperature of a heat exchanger,

for example, the inlet air and the outlet air of anevaporator.■ The electronic thermometer may be used to check wet-bulb(using a wet wick on one bulb) and dry-bulb temperatures.■ The condenser has three functions: to take the superheat outof the discharge gas, to condense the hot gas to a liquid, andto subcool the refrigerant.■ A typical condenser may subcool the refrigerant 10°F to20°F lower than the condensing temperature.■ Two types of metering devices are normally used on airconditioningequipment: the fixed bore (orifice or capillarytube) and the TXV.■ The fixed-bore metering device uses the pressure differencebetween the inlet and outlet of the device for refrigerant flow.It does not vary in size.■ The TXV modulates or throttles the refrigerant to maintain aconstant superheat.■ To correctly charge an air-conditioning unit, the technicianmust follow the manufacturer’s recommendations.■ The TXV system normally has a sight glass in the liquid lineto aid in charging. A subcooling temperature check may beused when no sight glass is available.■ SAFETY PRECAUTION: Before checking a unit electrically,the proper voltage and the current draw of the unit shouldbe known.■ The main electrical power panel may be divided into manycircuits. The air-conditioning system is normally on twoseparate circuits for a split system and one circuit for a packagesystem.■ When a hot compressor is started, assume that the system islow in refrigerant. A cylinder of refrigerant should be connected,so refrigerant may be added before the compressorshuts off again.

SUMMARY■ Summer air conditioning is sometimes added to an existingheating system. This is called add-on cooling.■ Different air volumes are sometimes desirable for the heatingand cooling seasons. The air in the heating season iswarmer at the terminal units when the air volume is reducedin the heating season.■ Different air volumes are accomplished with dampers andvariable fan speeds.■ The control circuit may have two transformers—one furnishedwith the furnace and one with the air-conditioning unit.■ When two power supplies (transformers) exist, the two maybe kept separated in the thermostat, or they may be wired inparallel and in phase.■ Package all-weather systems normally consist of gas heatand electric air conditioning or electric heat and electric airconditioning.

SUMMARY■ All compression-cycle refrigeration systems are similar toheat pumps; however, heat pumps have the capability ofpumping heat either way.■ A new component, the four-way reversing valve, enables theheat pump to reverse the refrigeration cycle and reject heat ineither direction.

■ Water to air is the term used to describe heat pumps that absorbheat from water and transfer it to air.■ Commercial buildings may use water to absorb heat fromone part of a building and reject the same heat to another partof the same building.■ Air-to-air heat pumps are similar to summer air-conditioningequipment.■ There are two styles of equipment: split systems and package(self-contained) systems.■ New names are applied to the heat pump components becauseof the reverse-cycle operation.■ The terms “indoor coil” and “outdoor coil” are also usedwith package heat pumps to avoid confusion.■ The refrigerant lines that connect the indoor coil with theoutdoor coil are the gas line (hot gas in winter and cold gasin summer) and the liquid line.■ The liquid line is always the liquid line; the flow reversesfrom season to season.■ Several metering devices are used with heat pumps. The firstwas the TXV. There may be two of them.■ Capillary tube metering devices are common. There maybe two of them, one for cooling and one for heatingoperations.■ A fixed-bore metering device that will allow full flow in onedirection and restricted flow in the other direction is used bymany manufacturers.■ The electronic expansion valve is used by some manufacturerswith close-coupled equipment because it will meter inboth directions and maintain the correct superheat.■ When standard filter driers are used with a heat pump installation,they must be placed in the circuit with the check valveto ensure correct flow. It must have a check valve piped in serieswith it, or when the flow reverses, it will backwash andthe particles will be pushed back into the system.■ The air-to-air heat pump loses capacity as the outside temperaturegoes down.■ At the balance point the heat pump alone will run constantlyand just heat the structure.■ Auxiliary heat is the heat that a heat pump uses as asupplement.■ Auxiliary heat is normally electric resistance heat. Oil andgas may be used in some installations.■ When the auxiliary heat is used as the only heat source, suchas when the heat pump fails, it is called emergency heat.■ Emergency heat is controlled with a switch in the roomthermostat.■ Coefficient of performance (COP) is determined from theheat pump’s heating output divided by the input. A COP of3:1 is common with air-to-air heat pumps at the 47°F outdoortemperature level. A COP of 1.5:1 is common at 0°F.■ The efficiency of a heat pump is a result of its being used tocapture heat from the outdoors and to pump that heat indoors.■ A heat pump is installed in much the same manner as a coolingair conditioner.■ The terminal air must be distributed correctly because it is notas hot as the air in oil or gas installations. Heat pump air normallyis not over 100°F with only the heat pump operating.■ SAFETY PRECAUTION: Provision for water drainage at the

outdoor unit must be provided in winter.■ The indoor fan must run when the compressor is operating,and the compressor operates in both summer and wintermodes.■ The four-way valve determines whether the unit is in theheating or cooling mode.■ The technician can tell which mode the unit is in by the temperatureof the gas line. It can get very hot.■ The space-temperature thermostat controls the direction ofthe hot gas by controlling the position of the four-way valve.■ Because the heat pump evaporator operates below freezing inthe winter, frost and ice will build up on the outdoor coil.■ When the system is in defrost, it is in the cooling mode withthe outdoor fan off to aid in the buildup of heat.■ Defrost is normally instigated (started) by time and temperatureand terminated by time or temperature.■ The refrigerant charge is normally critical with a heat pump.■ The use of scroll compressors increases the efficiency of heatpump systems.

SUMMARY■ Energy is transferred daily to and from the earth by solarradiation, rainfall, and wind.■ Geothermal heat pumps use the earth, or water in the earth,for their heat source and heat sink.■ Because the earth’s underground temperature in the summeris cooler than the outside air, heat loads from summer airconditioning can be rejected underground more efficiently.■ Geothermal heat pumps are very similar to air source heatpumps in that they both use reverse-cycle refrigeration.■ Geothermal heat pumps are classified as either open- orclosed-loop systems.■ Water quality is one of the most important considerations inthe design of an open-loop geothermal heat pump system.■ Open-loop systems usually use well water as their heatsource and heat sink. The water is then returned to the earthin some way. Heat exchanger fouling can be a problem ifwater quality is poor.■ Water sources for open-loop systems may be an existing wellor a new well. A well pump delivers the water from the wellto the heat pump. Wells have many categories.■ Pressure tanks are used in conjunction with wells in openloopsystems.■ Closed-loop heat pump systems recirculate the same antifreezefluid in a closed loop. This eliminates water-qualityproblems.■ Closed-loop or earth-coupled systems are used where thereis insufficient water quality or quantity or where local codesprohibit open-loop systems.■ The ground loop for closed-loop systems can either be avertical, horizontal, slinky, or pond/lake type. Loops can alsohave series or parallel fluid flows.■ The buried piping or underground heat exchanger is usuallyeither polyethylene or polybutylene pipe. Both of these materialscan be heat welded by a heat fusion process.■ The antifreeze solutions inside the buried piping are used toprevent freezing of the heat pump heat exchanger and forheat transfer purposes. Some southern climates do not needan antifreeze additive.

■ The water-to-water heat pump is becoming popular for use inradiant heating systems.■ Water-to-water heat pump systems often use a buffer tankto store the heated water until it is needed by the heatingcircuits.■ Water-to-water heat pump systems often have three circulatorpumps: one on the ground-water circuit, one between theheat pump and the buffer tank, and one between the buffertank and the heating circuits.■ Waterless heat pump systems utilize buried refrigerant linesinstead of buried water lines.■ Waterless heat pump systems transfer heat into and out ofthe refrigerant by using the ground as the heat source in thewinter and as the heat sink in the summer.

SUMMARY■ Heat enters the refrigerator through the walls of the box by conduction,by convection, and by warm food placed in the box.■ Evaporator compartments can be natural draft or forced draft.■ The evaporator in the household refrigerator operates at thelow-temperature condition, yet maintains food in the freshfoodcompartment.■ Sharp objects should never be used when manually defrostingthe evaporator.■ Evaporators may be flat-plate type or fan-coil type.■ Evaporators may be manually defrosted or have an automaticdefrost feature.■ Many compressors have a suction line, a discharge line, a processtube, and two oil cooler lines, all protruding from the shell.■ Many compressors in refrigerators do not have service ports.■ Most domestic refrigerators use the capillary tube meteringdevice.■ Current model refrigerators have a magnetic strip gasketwith a compression seal around the door or doors.■ The space-temperature thermostat controls the compressor.■ Most cabinet frost and moisture prevention heaters are small,electrically insulated wire heaters that are mounted againstthe cabinet walls near the door openings.■ The fans used for forced-draft condensers and evaporatorsare typically prop-type with shaded-pole motors.■ Ice makers are located in the low-temperature compartmentand freeze water into ice cubes.■ The service technician should not routinely apply gages to adomestic refrigerator system. Explore all other troubleshootingtechniques before applying gages.■ A very small amount of refrigerant lost from a refrigeratorwill affect the performance. Very small leaks may be foundonly with the best leak detection equipment.■ An epoxy may be used to seal a leak in an aluminum evaporator.■ Tubing in condensers is usually made of steel. These leaksshould be repaired with the appropriate solder.■ When a leak has been repaired, a triple evacuation should bepulled on the entire system.■ Under certain conditions capillary tube metering devicesmay be repaired.■ CRefrigerant should be recovered and never exhaustedinto the atmosphere. C

SUMMARY

■ Freezers are different from refrigerators because they operateonly as low-temperature refrigeration systems.■ Freezers must be level.■ Domestic freezer cabinet boxes may be of an upright designwith the doors swinging out or a chest-type with a lid that raises.■ These freezers are designed to operate in normal householdtemperatures and should not be located where temperaturesreach hot or cold extremes.■ Door gaskets must remain tight fitting, or air leaks will occur,causing the compressor to run excessively and frost tobuild up inside the cabinet.■ Many freezers have manual defrost because the doors are notopened as often, and defrost is not needed as frequently.■ Plate-type evaporator design uses the evaporator as a shelf,and another type uses the wall of the interior of the box as theevaporator plate.■ Compressors can be rotary or reciprocating.■ The capillary tube is the typical metering device for domesticfreezers.■ The condenser should be able to condense refrigerant at 25°Fto 35°F higher than the ambient air. The more efficient thecondenser, the closer the condensing temperature is to the airpassing over it.■ Compressors are air or refrigerant cooled. An air-cooledcompressor typically will have fins.■ Normally a wiring diagram is fastened to the back of the cabinet.This should be studied before you service the freezer.■ When servicing the freezer, check the forced-draft evaporatorand condenser fans to ensure that they are operating properly.■ If food has spoiled, odor may be a problem. If the insulationis fiberglass and has been saturated, it is possible the odorcannot be eliminated.■ Before a freezer is moved, the food must be removed andplaced where it will stay frozen.

SUMMARY■ Room air conditioners may be designed to be installed inwindows or through the wall.■ These units may be designed for cooling only, cooling andheating with electric strip heat, or cooling and heating with aheat pump cycle.■ The four major components in the cooling cycle for theseunits are the evaporator, compressor, condenser, and meteringdevice.■ Most units are designed to produce a heat exchange betweenthe capillary tube and the suction line. This adds superheat tothe suction line and subcools the refrigerant in the capillarytube.■ The heat pump cycle uses the four-way valve to redirect therefrigerant.■ The heat pump compressor is different from one found in acooling-only unit. It must have enough pumping capacity forlow-temperature operation.■ Before installing a unit, the technician should make sure thatthe electrical service is adequate.■ When installing these units, ensure that there is no possibilityof direct recirculation of air through the unit.■ The selector switch is the primary control for room airconditioningunits.

■ The primary maintenance for these units involves keepingthe filters and coils clean.■ Gages should be installed for service only when it is determinedthat it is absolutely necessary.■ Electrical service may involve the fan motor, thermostat, selectorswitch, compressor, and power cord.

SUMMARY■ A chiller refrigerates circulating water.■ The compression cycle chiller has the same four basic componentsas other refrigeration systems discussed previouslyin this text: the compressor, evaporator, condenser, and meteringdevice.■ R-22, R-134a, and other refrigerants which are environmentallyfriendly alternatives are used in reciprocating compressorchillers.■ Cylinder unloading is used to control the capacity of a reciprocatingcompressor.■ Rotary screw compressors are used for larger-capacitychillers using high-pressure refrigerants.■ These compressors are lubricated with an oil pump and separatemotor.■ The evaporators used for high-pressure chillers are eitherdirect-expansion or flooded evaporators.■ The condenser for high-pressure chillers may be either wateror air cooled.■ Many condensers have subcooling circuits that reduce theliquid temperature.■ The condenser, like the evaporator, has an approach relationshipbetween the refrigerant condensing temperature and theleaving-water temperature.■ Air-cooled condensers eliminate the need for using watertowers.■ Centrifugal compressors may be manufactured so that theycan be operated in series; this is called multistage operation.■ For prelubrication of the bearings, the oil pump on a centrifugalcompressor is energized before the compressor isstarted.■ The orifice or the high- or low-side float metering device istypically used for low-pressure chillers.■ When a centrifugal uses a low-pressure refrigerant, the lowpressureside is always in a vacuum. If there is a leak, air willenter the system.■ Absorption refrigeration is a process that uses heat as thedriving force rather than a compressor.■ The absorption chiller uses water as the refrigerant.■ The absorption chiller uses a salt solution consisting oflithium-bromide (Li-Br) as the attractant in the refrigerationprocess.■ These solutions are corrosive, and air must be kept fromthem.■ The absorption chillers also have a purge system.■ Many motor controls include motor overload protectiondevices, load-limiting devices, anti-recycle control, phasefailure protection, voltage unbalance, and phase reversalprotection.

SUMMARY■ The cooling tower rejects heat that has been absorbed into

the chilled water system.■ Cooling towers lower the temperature of the water in a towerby means of evaporation.■ Cooling towers should be protected from fire.■ The design of a cooling tower provides for distinct airflowpatterns.■ Fan drives for forced-draft towers may be belt or gear type.■ The cooling tower sump needs to be flushed periodically.■ Sumps may have heaters to protect from freezing.■ Cooling towers must have makeup water systems.■ The water flow through the tower must follow the pattern designedby the manufacturer.■ Larger pumps may have single- or double-inlet impellers.■ Most pumps for cooling towers are manufactured of cast iron.■ Vortexing (whirlpooling) may occur in the sump. This is notgood because air may be introduced into the pump.■ A tower bypass valve helps to maintain the correct towerwater temperature at the condenser.

SUMMARY■ The operation of chilled-water air-conditioning systems involvesstarting, running, and stopping the chiller systems inan orderly manner.■ When starting a chilled-water system, first check for sufficientchilled-water flow. If the system is water-cooled, checkfor condenser water flow. The interlock circuit through thecontactors must be satisfied; the cooling tower fan shouldstart, followed by the compressor. There may be a time delaybefore the compressor starts.■ The reciprocating, scroll, and rotary screw compressors maybe either air or water cooled.■ The centrifugal chiller will have a separate oil lubricationsystem. It should be verified that the lubrication system isfunctioning satisfactorily before starting the compressor.■ After the chiller is on and operating, the technician shouldobserve the operation for a period of time to ensure that it isall operating correctly.■ Water-cooled chillers must have water treatment to preventminerals and algae from collecting and forming.■ Inspecting and cleaning the water tower should be done on aregular basis.■ Water-cooled condenser tubes should be checked at leastannually. If they are found to be not clean or to have ascale buildup, they must be cleaned either with a brush orchemically.■ Condenser and evaporator tubes may be checked for defectswith an eddy current test instrument.■ Absorption chilled-water system and compression cyclesystem start-up are similar in many respects. Condenser andchilled-water flow must be established before the chiller isstarted. The cooling tower water must not be too cold or theLi-Br may crystallize.■ Absorption chillers must be observed for proper operation ona more regular basis than compression cycle chillers becausethey can be more intricate.■ The purge system may require more maintenance than othersystems on the absorption chiller. The vacuum pump oilshould be changed regularly.■ Technicians who maintain chillers should stay in contact

with the manufacturers of the equipment for the latest informationadvice, and the schedule for service schools.