Refrigeration Study Guide II

Unit

Unit Overview

Expansion Devices

The expansion device is often called the meteringdevice, and certain types may be referred to as expan-sion valves. This is a small component but one of the fournecessary for the refrigeration cycle to function. It can bea valve or a fixed-bore type and is one of the dividingpoints between the high- and low-pressure sides of thesystem. The compressor is the other component separat-ing the high- and low-pressure sides.

The expansion device is located in the liquid linebetween the condenser and the evaporator, usually at theinlet to the evaporator. Its function is to meter the liquidrefrigerant into the evaporator. The three types of devicesused on modern equipment are the thermostatic expan-sion valve, the automatic expansion valve, and the fixed-bore type such as a capillary tube.

The thermostatic expansion valve meters the refrig-erant to the evaporator using a thermal sensor to moni-tor the superheat at the suction line. Electronic expansionvalves (EEVs) use a solid-state controller to instruct astepper motor to control the modulation of the valve'sport. Thermistors act as one of the inputs to the controllerfor evaporator superheat control. The stepper motor canact in any direction at 200 steps per second. The auto-matic expansion valve meters refrigerant to the evapora-tor by using a pressure-sensing device that maintains aconstant pressure in the evaporator. The capillary tube isa fixed-bore metering device that has no moving parts. Itcontrols refrigerant flow by pressure drop. This may be inthe form of a small diameter tube, which in some appli-cations can be quite long.

Key Terms

AlgorithmsAutomatic Expansion ValveBalanced Port TXVCapillary TubeCross Liquid Charge BulbCross Vapor Charge BulbDual Port TXVElectronic Expansion ValveError

Expansion (Metering) DeviceExternal Equalizer \^/Feedback LoopsFixed-Bore DeviceLiquid Charge BulbOffsetPressure Limiting TXVProportional, Integral, and

Derivative (PID) Controller

Refrigerant ReceiverStep Motor Electronic

Expansion ValvesThermostatic Expansion Valve

(TXV)Vapor Charge Bulb

REVIEW TEST

Name Date Grade

Circle the letter that indicates the correct answer.

1. The thermostatic expansion valve regulatesrefrigerant flow to the evaporator based on:A. heat of compression.(B. suction line superheat.C. external equalizer pressure.D. evaporator pressure.

2. The capillary tube is a type of:k. external equalizer.

(J3.' metering device.C. TXV sensor.D. device that senses superheat.

Refrigeration & Air Conditioning Technology

•

3. TheTXV sensing bulb is mounted:A. on the liquid line between the condenser

and the TXV.EL at the inlet to the condenser.C.< on the suction line between the evaporator

and compressor.D. on the compressor discharge line.

4. An external equalizer is used when:A. the pressure drop across the evaporator is

excessive.B. the liquid line pressure becomes too great.C. the receiver is too full of refrigerant.D. the pressure drop at the automatic expan-

sion valve becomes too great.

5. When the load on the evaporator increases,the TXV:(A) increases the flow of refrigerant.B. decreases the flow of refrigerant.C. maintains the flow of refrigerant.D. decreases the pressure across the evapora-

tor.

6. The liquid charge bulb is:A. a sensing bulb on an automatic expansion

valve.B. a bulb attached to one end of a capillary tube.C. a sensing bulb at the inlet of the expansion

valve.a TXV sensing bulb charged with a fluidsimilar to that of the system refrigerant.

7. Superheat is:(Ay the sensible heat absorbed by the refriger-

ant after it has boiled to a vapor.B. the heat of compression at the compressor.C. heat used to boil the liquid in the evapora-

tor.D. latent heat given off by the condenser.

8. The sensing bulb and transmission tube area part of the:A. automatic expansion valve.B. capillary tube.C. king valve.

© TXV-

9. A small amount of superheat in the suctionline is desirable with a TXV to:A. keep the proper amount of refrigerant in the

receiver.B. insure the proper head pressure at the con-

denser.C. keep from starving the evaporator.

;D. insure that no liquid refrigerant enters thecompressor.

10. The thin metal disc connected to the needlein the TXV is called the:A,, spring. C. seat.

/ By diaphragm. D. sensing bulb.

11. Liquid refrigerant should be completelyboiled to a vapor:A. close to the inlet of the evaporator.B. approximately halfway through the evapo-

rator.C. near the outlet of the evaporator.D. halfway through the suction line.

12. The cross liquid charge bulb at the TXV con-tains fluid that:A. has similar characteristics to the system

fluid to prevent liquid refrigerant from enter-.~ ing the suction line.

! B.) has different characteristics from the sys-tem fluid and helps prevent liquid refriger-ant from flooding over to the compressor.

C. causes the valve to stay open during the offcycle.

D. follows the typical pressure-temperaturerelationship.

13. Balanced portTXVs are used:A. to feed refrigerant at a normal rate with low

ambient temperatures.B. to feed refrigerant at a normal rate with high

ambient temperatures.C. to stop refrigerant flow during low ambient

temperatures.D. to stop refrigerant flow during high ambient

temperatures.

14. The pressure-limiting TXV:A. allows the compressor to operate at low

temperatures.B. shuts off the condenser fan during a hot

pull down.C. continues to feed refrigerant to the evapo-- rator during a hot pull down.

D. shuts off the refrigerant flow to the evapo-rator when it has reached a predeterminedpressure.

15. The automatic expansion valve was de-Signed to:A. maintain a constant pressure in the evapo-

rator.B. meter refrigerant to the evaporator with an

electronic sensing device.C. reduce refrigerant flow when the evaporator

pressure drops.D. vary the pressure in the evaporator under

low ambient conditions.


716. What force is cancelled out when using a

balanced port TXV?A. Liquid forceB. Evaporator forceC. Bulb forceD. None of the above

17. What type of TXV uses a large port for pull-down capacities and a smaller port forholding loads?A. Balanced portB. Liquid charged£. Cross charged(ll) Dual port

18. Which type of valve uses a control board,transistors, thermistors, and a steppermotor controlled by an algorithm?

(A.) Electronic expansion valveB. Balanced port valveC. Dual port valveD. None of the above

19. The difference between the superheat setpoint of an electronic expansion valve andthe actual superheat is called:A. An errorB. An algorithmC. A rangeD. A differential

20. The terms offset and error are one and thesame.

00 True B. False


REVIEW TEST

Name Date Grade


1. Two-temperature operation of a refrigera-tion system is necessary when:A. the compressor must be protected from

overloading.B. more than one evaporator, each at a differ-

ent temperature, is operating from onecompressor.

C. the coil in the evaporator is excessively

£-> Ion9-/DJ a multiple-circuit distributor is used.

2. The EPR valve is installed in the suction lineat the evaporator outlet and it:A. modulates the suction gas to the compressor.B. will let the evaporator pressure go only as

low as a predetermined point.C. will provide the same service as an automat-

ic expansion valve when coupled with a TXV.D. all of the above.

3. Normally there is a gage port known as agage port installed in the EPR

valve body.two-temperatureSchrader

C. low ambientD. one-time

4. The crankcase pressure regulator (CPR) isinstalled in the suction line near the:

Qv) compressor.B. evaporator.C. EPR.D. multiple-circuit distributor.

5. A hot pull down is when:A. there is excessive ice on the evaporator.B. the condenser has been flooded.C. the metering device is starving the evaporator.

(6) the temperature of the load is high and thecompressor has to run for a long period oftime to lower the temperature.

6. A valve used to protect the compressor dur-ing a hot pull down is the:A. CPR valve. C. TXV.B. EPR. D. gage manifold.

7. A one-time relief valve is constructed with:A. a fusible plug.B. an adjustable spring.C. a Schrader port.D. a two-temperature mechanical valve.

8. A low ambient control is used tom cold weather.

(A) maintain an acceptable head pressureB. lower the compressor crankcase tempera-

tureroute refrigerant to the receiverC.

D.

9.

reduce refrigerant flow to the evaporator

is a type of low ambient tempera-

10.

ture head pressure control:A. CPR C. EPR

[B.) Fan cycling D. Off-cycle defrost

is another type of low ambienttemperature head pressure control:

Air volume control using shutters anddampersPlanned defrostPumping down the system using the kingvalveInternal heat

B.C.

D.

11. The solenoid valve is frequently used tocontrol fluid flow. This valve:A^ has a slow reaction time.B.: has a fast or snap action.C. is used to control fan speed.D. is a normally open valve.

12. Condenser flooding may be used:A. for compressor protection.B. to insure sufficient oil in the compressor

crankcase.to keep liquid refrigerant from the compressor,to control head pressure in low ambienttemperature conditions.

QD.

13. One use for the low-pressure switch is:(A) for low charge protection.B. to keep liquid refrigerant from the compressor.C. to throttle refrigerant to the compressor.D. to keep the compressor from flooding.


1014. The high-pressure control:

A. shuts off the condenser fan when a high, pressure exists.

{^f shuts down the compressor when the headpressure is excessive.

C. insures that enough refrigerant reaches theevaporator.

D. controls the CPR at the compressor.

15. Random defrost is accomplished:A. with a timer.B. using a high-pressure control.C. using a low-pressure control.

(5) during the normal off cycle.

16. Defrost using internal heat is accomplishedwith:fi. a sail switch.(B.) hot gas from the compressor.C. electric heating elements.D. mullion heaters.

17. The receiver is located in the:A. suction line.J3, compressor discharge line.(C.) liquid line.D. evaporator outlets.

18. The king valve is normally located:i AJ between the receiver and the expansion

valve.B. at the evaporator outlets.C. between the compressor and the condenser.D. between the condenser and the receiver.

19. The suction line accumulator is located inthe suction line and its primary purpose isto collect:A./ liquid refrigerant and oil.B. contaminants and moisture.C. excess vapor refrigerant.D. acid produced by the compressor.

20. The oil separator is normally located be-tween the:A. condenser and the receiver.B. evaporator and the compressor.

,&^ receiver and the expansion valve.D. compressor and the condenser.

21. Electronic evaporator pressure regulatingvalves use a sensor in the refrigeratedcase's:

discharge air.return air.

C. evaporator outlet.D. evaporator inlet.

22. Electronic evaporator pressure regulatingvalves are powered by a(an):A. magnetic valve.B. electric valve.C. pressure.D. bi-polar step motor.

23. Low charge protection and control ofrefrigerated space temperature are the twomajor applications for a low-pressureswitch in refrigeration.

True B. False

24. On an automatic pump-down system, thethermostat controlling the liquid line sole-noid is located:A. on the evaporator.B. on the liquid line.C. in the outside ambient.D. in the refrigerated space.

25. Oil pump discharge pressure minuscrankcase pressure is:A. gross oil pressure.B. differential oil pressure.

(CJ net oil pressure.D. none of the above.

26. A relay wired to the load side of a contac-tor or motor starter which acts like aninductive-type ammeter and is sensitive tocurrent flow is:

(A.) the current sensing relay.13. the potential relay.C. the magnetic relay.D. none of the above.

27. Electronic oil safety controllers use ato sense net oil pressure.

A. thermistorB. transistorC. capillary tubeD. pressure transducer

28. The remote sensing bulb on a defrost ter-mination and fan delay switch is located:

(XA\ on the evaporator.B. on the fan housing.C. on the defrost heater.D. none of the above.

29. The oil return line connecting the oil sepa-rator to the compressor's crankcase shouldbe just above temperature mostof the time.A. compressor crankcaseB. dischargeC. evaporating

; D. roomV ,'


Key Terms

AlkalineAnalogAugerBacteriaBin SwitchCam SwitchCell-Type IceChloraminesCrescent-Shaped IceCylindrical-Shaped IceDigitalElectronic Erasable

Programmable Read-OnlyMemory (EEPROM)

Error Code

REVIEW TEST

FlightsFlush CycleFreezing CylinderHardnessIce Flake MachineIce QualityInfrared Electric EyeInputsInternetLight Emitting Diode (LED)Liquid FloodbackMicroprocessorOutputsPHPreventive Maintenance

ProtozoaPurge ValveReverse OsmosisSanitizingScale InhibitorSelf-DiagnosticSequence of EventsSiphonSonarTotal Dissolved SolidsTurbidityVirusesWeep HolesWet Compression

Name Date Grade


1. A type of material often used on evapora-tors because it is durable, very sanitary,and resists corrosion is:

brass. C. copper,stainless steel. D. plastic.

c 2. Cutting surfaces on an auger for a flake icemachine are called:Qv flights. C. knives.B. edges. D. blades.

e 3. A dirty evaporator from mineral depositson a flake ice machine will cause:£. high suction pressure.

(By< low suction pressure.C. high head pressure.D. quiet operations.

6. is made using a gear motorand auger?A. Cube iceB. Cylinder ice

4. The of an ice flake machinehas the highest failure rate.A. bin controlB. dump solenoidC. microprocessor

gear motor assembly

(C.) Flake iceD" Block ice

D.

5. A periodic way of ridding unwanted mineralbuild-up in the water of an ice machine is:A. a flush cycle.B. bin cleaning.C. a chemical treatment.D. none of the above.

, 7. Methods used for proper ice bin controlare:A. sonar. C. infrared eye.B. thermostats. D., all of the above.

/ 8. Ice production for a flake ice machinedepends on:A. inlet water temperature.B. surrounding air temperature.C. inlet water purity.D. both A and B.

> 9. Which type of ice is made inside a tubewithin a tube evaporator?A. Cell type ice C. Cylindrical iceB. Sheet ice ft). Flake ice

• 10. Pre-chilling the evaporator in an icemachine before the water pump comes onhelps prevent in the watersump.A. air bubbles C. slushB. mineral deposits (p.) all of the above

11. Most ice cube machines are defrosted by:A. Electric defrost. Q Ambient defrost.B. Natural defrost. D. Hot gas defrost.

12. Liquid refrigerant returning to the compres-sor while the compressor is operating iscalled:A. liquid slugging.B, migration.

i C.) liquid floodback.u. none of the above.

18. A buildup of minerals that forms a flakycoating on the surface of the evaporatorand water system on many ice makers is:A. slime.B. sediment.C. scale.D. none of the above.

13. On some ice machines, air is introduced byway of between the ice slaband the evaporator plate to release the suc-tion force between the evaporator and thejce slab.(/U weep holes C. gravityB. air pump D. water stream

14. As the low-side pressure drops on an icemachine, a reverse-acting low-pressurecontrol will its contacts at a setlow pressure.A. open ; B. \e

15. A small computer that has a sequence ofevents or algorithm stored in its memoryfor controlling the functions of many icemachines is called a:A. diode. C. transistor.B. transducer. D.) microprocessor.

16. The microprocessor will associate an icemaker malfunction with a(n) anddisplay it on a light emitting diode (LED)display.A. ' error codeB\e codeC. malfunction codeD. none of the above

17. Ice production, cycle times, and systemoperating pressures for an air-cooled icemachine depend on what two factors?A. air temperature entering the condenserB. water temperature entering the ice

machineC. relative humidity of the ambient airD. both A and B

19. The thermal cooling capacity of ice isreferred to as:Aj hardness. C. coolness.B. compactness. D. density.

20. Sanitizing an ice machine gets rid of:A. bacteria. C. protozoa.B. viruses. D. all of the above.

21. Cleaning an ice machine with an approvedice machine cleaner gets rid of:A. viruses. C. scale.B. bacteria. D. sediment.

22. Water conditions can be broken down into:A. suspended solids.B. dissolved minerals and metals.C. chemicals.D. all of the above.

23. Chemicals in water are removed by:A. sanitizing.B. cleaning.C. carbon filtration.Tb. reverse osmosis.

24. A dirty condenser on an ice machine willcause:A. high head pressure.B. low head pressure.C. low suction pressure.D. none of the above.

25. A restricted metering device on an icemachine will cause:A. high head pressure.B. high suction pressure.C. low suction pressure.D. none of the above.


I if.Unit

Special Refrigeration Applications

Unit Overview

Transport refrigeration is the process of refrigeratingproducts while they are being transported from one placeto another by truck, rail, air, or water.

Truck refrigeration systems include the use of ice forshort periods of time, dry ice (solidified and compressedcarbon dioxide), liquid nitrogen, liquid carbon dioxide(COz), Eutectic solutions, and compression-type refriger-ation systems.

Products shipped by rail are refrigerated with a self-contained unit located at one end of the refrigerated car.These are generally diesel-driven motor generator unitssimilar to those units used on trucks.

Extra-low-temperature refrigeration, below -10°F, isgenerally used to fast freeze foods on a commercial

basis. These temperatures may be as low as -50°F. Oftentwo stages of compression are used to achieve tempera-tures this low. For even lower temperatures, cascaderefrigeration may be used, which might include two orthree stages of refrigeration. When food is frozen, thefaster the temperature of the product is lowered, the bet-ter the quality of the food.

Ships that must have refrigeration systems for theircargo may have large on-board refrigeration systems ormay use self-contained units that are plugged into theship's electrical system.

For air cargo hauling, ice or dry ice is generally usedwith specially designed containers. On-board refrigera-tion systems would be too heavy.

Key Terms

AmmoniaCascade RefrigerationCarbon Dioxide (CO?)Dry IceEutecticExtra-Low-Temperature

RefrigerationLiquid NitrogenMarine RefrigerationMarine Water BoxesNose-MountPiggy-Back Cars

Quick FreezeRailway RefrigerationSublimationTransport RefrigerationTruck RefrigerationUnder-Belly Mount

REVIEW TEST

Name Date Grade


1. Dry ice is composed of:A. liquid nitrogen.B. liquid carbon dioxide.

(C.) solidified carbon dioxide.TlC solidified ammonia.

2. Sublimation is to change from a:A. liquid to a vapor.

; B. solid to a vapor.C. vapor to a solid.D. solid to a liquid.

3. Air in the atmosphere is approximately:A. 78% nitrogen.B. 21% nitrogen.C. 78% oxygen.D. 78% carbon dioxide.

4. An Eutectic solution is:A. a phase change solution.B. a very warm solution.C. an acid solution.D. an explosive solution.


5. Liquid nitrogen is used to:A. clean the inside of refrigerated trucks,

clean the tubes in marine refrigeration sys-tems.refrigerate products in a truck,provide the cooling in a standard kitchenrefrigerator.

B.

C.D.

6. Extra-low-temperature refrigeration is usedto:

insure that ice cream remains hard,quick freeze meat and other foods,provide refrigeration in large ships,provide refrigeration for meat in largesupermarkets.

B;C.D.

7. Cascade refrigeration:A. utilizes flowing water to provide refrigeration.B.) utilizes two or three stages for low-temper-

ature refrigeration.C. provides medium-temperature refrigeration.D. provides high-temperature refrigeration.

8. Condensers that have marine water boxeshave:A. removable water box covers.B. tubes made of cupronickel.C. tubes that can be cleaned.D. all of the above.

9. Dry ice changes state at:A. -44° F. C. -320° F.

25°F. D. -109°F.

10. Liquid nitrogen changes state at:A. -44°F -d- -320°F.B. 25° F. D.' -109°F.

11. Vapors given off from liquid nitrogen are:A. odorless.B. oxygen depriving.C. colorless.

• D.) all of the above.

12. A Compressor with capacity control will:A. operate at reduced capacity.B. operate at a higher capacity than rated.C. pump excess oil.D. need more horsepower than rated.

13. Most truck refrigeration systems:A. will never shut off.B. must be started up manually.(X will not operate in cold climates.

(D.) start and stop automatically.

14. Most transport refrigeration is sized:(A) to hold the load temperature only.B. to pull the load temperature down.C. to use maximum fuel for refrigeration.D. with no capacity control.

15. Quick freezing of foods:A. is never done because it changes the flavor.B. preserves the flavor and quality of foods.C. is only done in other countries.D. none of the above.

, 16. Chillers for ship refrigeration often circulatefor low-temperature refrigeration.

A. water.B. nitrogen.C. fish oil.D. brine.


n5. When the temperature is above 70°F, the

temperature difference between the ambientand the condensing temperature for moststandard units is approximately:A. 15°F. C. 30°F.B. 20°F. 'tf 45°F.

6. In a wastewater water-cooled system, thetemperature difference between the con-densing refrigerant and the leaving watertemperature is approximately:A. 10°F. C. 30°F.B. 20°F. /D. varies.

7. In a recirculating water-cooled system, thetemperature difference between the waterentering and the water leaving the condens-

, er should be approximately:( A; 10°F C. 30°F& 20°F. D. 40°F.

8. If there is a low refrigerant charge in a sys-tem using a capillary tube, the:A. suction and discharge gages will both indi-

cate a high pressure.B. suction and discharge gages will both indi-

cate a low pressure.C. suction gage will indicate a higher-than-

normal reading and the discharge gage willindicate a lower-than-normal reading.

D. suction gage will indicate a lower-than-nor-mal reading and the discharge gage willindicate a higher-than-normal reading.

9. When the compressor in a system with acapillary tube is sweating, it is a sign of:A./ refrigerant overcharge.BT a malfunctioning crankcase heater.C. a malfunctioning king valve.D. all of the above.

B.

C.

10. Three major functions of a condenser are todesuperheat the hot gas, condense therefrigerant, and:A. pump the refrigerant to the expansion

valve.reduce the pressure of the refrigerantentering the evaporator,absorb heat from the ambient air.subcool the refrigerant before it leaves thecoil.

11. The condenser should not be located wherethe fan discharge air is:A. subcooled.B.) recirculated.

"C'.' partially vaporized.D. superheated.

12. If a sight glass shows bubbles during a nor-mal operation, it indicates:A. an overcharge of refrigerant.B. a low charge of refrigerant.

13. When an evaporator has a water coil totransfer heat from, the temperature differ-ence between the evaporating temperatureand the leaving water temperature is calledthe:A. arrival.B. delta.

( C.' approach.D. none of the above.


Refrigeration Study Guide II

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