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LESSON

1 LECTURE

INTRODUCTION TO COMPRESSORS

SUB-OBJECTIVE

At the end of this lesson the tr inee !ill "e "le to#

1$ Identif% the t%&es 'o(&ressors )sed in ir 'onditionin* ndrefri*er tion$

+$ Identif% their & rts nd f)n'tions,

$ Corre'tl% tro)"leshoot for ( .or nd (inor &ro"le(s$

/$ Corre'tl% ( int in the s id 'o(&ressors$

1$0 LAS O2 RE2RI3ERATION

The compression system is the basis of operation of the refrigeration unitsdescribed in this chapter.

One must understand the system to accurately diagnose (identify) mechanicaldifficulties.

Many types of compression mechanisms are explained to help the service

technician become familiar with their basic operations.

All refri*er tin* s%ste(s de&end on fi4e ther( l l !s#

1. Fluids absorb heat while changing from a li uid state to a vapor stateand give up heat in changing from a vapor to a li uid.

!. The temperature at which a change of state occurs is constant duringthe change provided the pressure remains constant.

". #eat flows only from a body which is a at a higher temperature to a

body which is at a lower temperature (hot to cold)

$. Metallic parts of the evaporating and condensing units use metals%which have a high heat conductivity (copper% brass% aluminum).

$. #eat energy and other forms of energy are interchangeable.

2OR E5AMPLE#

Ele'tri'it% ( % "e 'on4erted to he t6 he t to ele'tri' l ener*% ndhe t to (e'h ni' l ener*%$

MO&' $ *+, -O &+T+O + / * & , F,+/ ,*T+O-OM0, +O 2 T M * & -OM0, O, O 1 0*/ 1

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+$0 COMPRESSION C7CLE

The compression cycle is so named because it is the compressor% whichchanges the refrigerant vapor from low pressure to high pressure.

This pumping causes the transfer of heat energy from the inside of the cabinetto the outside. ince the compression machine transfers heat from one placeto another% it may also be called a heat pump.

* refrigerating system consists principally of a high pressure side and a low3pressure side Fig. $3131.

* refrigeration cycle follows these steps4 From the li uid receiver% /% li uid

*+, -O &+T+O + / * & , F,+/ ,*T+O MO&' $O 1 0*/ ! -OM0, +O 2 T M * & -OM0, O,

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refrigerant% at a high pressure% flows through the refrigerant control% *% (apressure reducer).

+t moves into the evaporator% 5. The evaporator is under a low pressure.#ere the li uid refrigerant vapori6es (boils) and absorbs heat.

The low3pressure side extends from the refrigerant control% *% throughevaporator 5.

Then to the compressor inta7e valve% -

Then the high3pressure side begins in the cylinder above the piston% &% on thecompression stro7e.

+t extends from the exhaust valve% % through the condenser% F% and the li uidreceiver% /% and into li uid line% to the refrigerant control% *.

The vapor then flows into the compressor through the inta7e valve% -% andbac7 into the compressor cylinder.

The piston% &% on the compression stro7e% s uee6es the vapor into a smallspace with an increase in temperature.

2i*$ /-1-+$Ill)str tes this &rin'i&le$

2i*$ /-1-+$ The he t of the 4 &or is 'o(&ressed into s( ll s& 'e nd r isesthe 4 &or te(&er t)re *re tl%$

A-V1 8 Vol)(e of 4 &or t the end of the int 9e stro9e

This 8 : ')$ in$ ;1 1 '(

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hi'h 8 The te(&er t)re of the 4 &or t end of theint 9e stro9e

hi'h8 =0 2$ ;10 C$

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2i*$ /-1- $ Co(&ression '%'le sho!in* the flo! of refri*er nt$

The "o4e Ill)str tes t%&i' l 'o(&ression '%'le s )sed in do(esti'

MO&' $ *+, -O &+T+O + / * & , F,+/ ,*T+O-OM0, +O 2 T M * & -OM0, O, O 8 0*/ 8

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refri*er tor$

1. vaporator. !. uction line. ". -ompressor

$. -ondenser 8. -apillary tube% * to 5.

9. *ccumulator

/$0 TEMPERATURE AND PRESSURE CONDITIONS IN T?E COMPRESSIONC7CLE

:hen the compressor starts% it moves molecules of refrigerant from the low3pressure side to the high3pressure side without much difficulty. *fter thischange% the modules are not moving about much faster.

See 2i*$ /-1-/B$

These molecules of refrigerant enter the condenser from the compressor through opening at 1. The temperatures are the same (;< deg. F.) inside andout.

0ressure is the sum of the bombarding molecules and temperature is thespeed of molecular motion.

+t is necessary then to speed up the molecules. This will raise their temperature to where they can give up heat to surrounding cooling surfaces( air and water ).

The longer the compressor runs% the more vapor molecules it s uee6es intothe condenser.

:ith each stro7e% the pressure and temperature increase since moremolecules are hitting the sides of the container.

The compressor piston% pushing the vapor molecules against the higher pressure% hits them harder% speeding them up (increasing temperature).

&uring compression% the pressure increases (due to 5oyle=s aw).

*t the same time% the temperature increases ;e@&l ined "% Ch rles L !,