8/10/2019 3air con02

1/12

8/10/2019 3air con02

2/12

8hile flowing through the con#enser it is coole#, gives up the heat that ita$sor$e# in the evaporator an# returns to a li&ui#. /t then flows into the li&ui#receiver rea#' to repeat the c'cle.

The motor control thermal element is clampe# to the en# of the evaporator atthe $eginning of the suction line.

After the evaporator is coole# to its proper temperature, the control $ul$pressure causes the motor control to turn off the current to the motor. The

compressor is stoppe#.

The operating characteristics of this s'stem are &uite satisfactor'. Therefrigerant oil is circulate# without trou$le. The temperature control limits canalso $e *ept &uite close.

This t'pe refrigeration c'cle is use# wi#el' in small commercial applications.4ecause the pressures #o not $alance on the off c'cle, the motor compressormust start un#er loa#.

/f the nee#le or seat in the expansion valve is fault' an# refrigerant lea*s

through the valve on the off c'cle, li&ui# refrigerant ma' flow into the suctionline.

8hen the compressor starts, frosting of the suction line will in#icate this. /fthe trou$le is severe, it ma' result in li&ui# refrigerant entering the compressorthrough the suction line.

This )a& (a'se the (o)*ressor to 6no(6 se/ere!&%

A/0 "1/T/1/12 0EF0/2E0AT/1 +%E 3%E551 7A2E 4A5/" 0EF0/2E0AT/1 565TE+5

8/10/2019 3air con02

3/12

4i+% ,-2-$% Co)*ression s&ste) 'sin+ a'to)ati( e7*ansion /a!/e refri+erant(ontro! 8AEV9

+%E 3 A/0 "1/T/1/12 0EF0/2E0AT/14A5/" 0EF0/2E0AT/1 565TE+ %E551 7A2E 3

8/10/2019 3air con02

4/12

8/10/2019 3air con02

5/12

8/10/2019 3air con02

6/12

%i&ui# refrigerant flows from the con#enser up through the li&ui# line to thefilter (which ma' also $e a #rier).

From the filter, refrigerant flows through the capillar' tu$e refrigerant controlinto the evaporator. The pressure of the li&ui# refrigerant, as it enters thecapillar' tu$e at the filter en#, is at a high pressure.

This is the hi+h-*ress're side% The *ress're in the e/a*orator is !o%

The #esign of the capillar' tu$e is such that it maintains a pressure #ifferencewhile the compressor is operating. The compressor maintains a low pressurein the evaporator an# the refrigerant $oils, rapi#l' a$sor$ing heat.

The vaporie# refrigerant moves through the suction line $ac* to thecompressor. ere it is compresse# to a high pressure an# #ischarge# into thecon#enser.

It is (oo!ed in the (ondenser and ret'rns to a !i

8/10/2019 3air con02

7/12

4i+% ,-2-,% Co)*ression s&ste) 'sin+ (a*i!!ar& t'"e t&*e refri+erant (ontro!%

+%E 3 A/0 "1/T/1/12 0EF0/2E0AT/14A5/" 0EF0/2E0AT/1 565TE+ %E551 7A2E =

8/10/2019 3air con02

8/12

0%1 MULTIPLE EVAPORATOR SYSTEM

5ome commercial refrigerating s'stems have one con#ensing unit connecte#to two or more evaporators.

%i&ui# refrigerant flows through the thermostatic expansion valves to theevaporators.

The evaporators ma' have the same evaporator temperatures or the' ma'evaporate the refrigerant at #ifferent temperatures.

/f the evaporator temperatures are the same, the s'stem uses onl' a low-si#efloat or the thermostatic expansion valve to control the refrigerant.

/f two or more evaporating temperatures are #esire#, a froen foo#stemperature an# a water cooling temperature (for example), a #evice must $euse# to *eep one of the evaporators at a higher low-si#e pressure.

%oo* at schematic, Fig. 3--9.

A two-temperature valve in the suction line (upper left) *eeps the low-si#epressure refrigerant li&ui# an# vapor in evaporator 4 at a higher pressure thanat evaporator A.

The evaporator temperature is governe# $' the evaporating pressure Thelower the pressure, the lower the temperature.

A/0 "1/T/1/12 0EF0/2E0AT/1 +%E 3%E551 7A2E > 4A5/" 0EF0/2E0AT/1 565TE+5

8/10/2019 3air con02

9/12

8/10/2019 3air con02

10/12

A li&ui# in#icator (slight glass) is often inclu#e# in the li&ui# line. The servicetechnician ma' then chec* to see if there is enough refrigerant in the s'stem.4u$$les will in#icate a refrigerant shortage this s'stem, as shown uses apressure motor control. The operating pressure is ta*en from the low si#e ofthe s'stem.

A line from the high-pressure si#e also enters the motor control. This operatesa safet' #evice which stops the motor if the con#ensing pressure (high si#e)

goes too high.

+ultiple (two or more) evaporator refrigeration s'stems are commonl' use# incommercial refrigeration applications.

=%1 COMPOUN; RE4RIERATIN SYSTEMS

/n compoun# refrigerating s'stems, two or more compressors are connecte#in series, Fig. 3--;.

In this i!!'stration#

Co)*ressor No% $ dis(har+es into the inta6e side of(o)*ressor No%2%

Co)*ressor No% 2 then dis(har+es into the(ondenser%

:ere the /a*or (ondenses then the !i

8/10/2019 3air con02

11/12

4i+% ,-2-=% Co)*o'nd refri+eratin+ s&ste)%

From the li&ui# receiver the li&ui# refrigerant flows up to the thermostaticexpansion valve an# into the evaporator.

+%E 3 A/0 "1/T/1/12 0EF0/2E0AT/14A5/" 0EF0/2E0AT/1 565TE+ %E551 7A2E !!

8/10/2019 3air con02

12/12

/n the evaporator the refrigerant $oils an# a$sor$s heat. From the evaporatorthe vaporie# refrigerant flows $ac* to compressor 1o.!. From here the c'cleis repeate#.

5uch a compoun# s'stem increases capacit' then, pulling #own to such a lowpressures (low temperature) that one compressor cannot #o it well.

0efrigerant vapor is not con#ense# $etween compressors. An inter coolerlowers the vapor temperature. This t'pe of installation usuall' re&uires an oil

separator for each compressor.

A single-temperature motor control operates all motors an# a thermostaticexpansion valve controls the li&ui# refrigerant flow into the evaporator.

5ince the pressures #o not $alance on the off c'cle, motors capa$le of startingun#er loa# are re&uire#.

"ompoun# installations usuall' operate un#er rather heav' servicere&uirements. "on#ensers an# refrigerant must $e *ept clean. "ompressorvalves must $e *ept in goo# con#ition.

A/0 "1/T/1/12 0EF0/2E0AT/1 +%E 3%E551 7A2E ! 4A5/" 0EF0/2E0AT/1 565TE+5