2–19
62-11637
2.13 REFRIGERANT CIRCUIT - HEATING AND
DEFROSTING
When vapor refrigerant is compressed to a high pres-
sure and temperature in a reciprocating compressor,
the mechanical energy necessary to operate the com-
pressor is transferred to the gas as it is being com-
pressed. This energy is referred to as the “heat of
compression” and is used as the source of heat during
the heating cycle.
When the system calls for heating (see
• the normally closed hot gas solenoid valve (SV4)
is energized (opened).
• the normally open condenser pressure control
solenoid valve (SV1) is energized (closed).
• the normally closed liquid line solenoid valve
(SV2) is de-energized (closed)
Flow of hot discharge gas from the compressor enters
the evaporator.
The refrigerant is warmer than the air that is circulated
over the tubes by the evaporator fan. The evaporator
tubes have aluminum fins to increase heat transfer;
therefore heat is transferred to the air circulated over
the evaporator. This warm air is circulated throughout
the refrigerated compartment to maintain the cargo at
the desired temperature.
When additional heating capacity is required the nor-
mally closed Liquid Line Solenoid valve (SV2) is ener-
gized (opened) to allow additional refrigerant to be
metered into the hot gas cycle (through the evaporator
expansion valve). Refrigerant will be forced from the
receiver (even though SV1 is closed) by the hot gas
bypass line which functions to raise the receiver pres-
sure above evaporator pressure.
If the discharge pressure rises to 350 psig (23.8 bar)
when in defrost or 390 psig (26.5 bar) when in heating,
SV1 will be de-energized momentarily to lower the dis-
charge pressure.
Figure 2.11 Refrigeration Circuit - Heat and Defrost
BYPASS
CHECK
VALVE
RECEIVER
FUSIBLE PLUG
FILTER-DRIER
HEAT
EXCHANGER
VIBRASORBER
DISCHARGE
CHECK VALVE
SUBCOOLER
LIQUID LINE
SERVICE VALVE
SV1
SV2
N/O
N/C
HPS
CDP
COMPRESSOR
CSMV
CSP
EVAPORATOR
CDT
CST
EVOP
EVOT
VIBRASORBER
N/C
SV4
EVXV
DISTRIBUTOR
',6&+$5*()/2:
68&7,21)/2:
$'',7,21$/ 5()5,*(5$17
3$7+:+(169,623(1('
CONDENSER
DRAIN PAN
MM
POSITION
VARIES
Summary of Contents for Transicold X4 7300
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