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2.12 REFRIGERATION CIRCUIT DURING COOL-
ING
When cooling, (See
vapor compression refrigeration system. The main
components of the system are: the (1) reciprocating
compressor, (2) air-cooled condenser, (3) evaporator
expansion valve and (4) direct expansion evaporator.
The compressor raises the pressure and the tempera-
ture of the refrigerant and forces it through the dis-
charge check valve into the condenser channels. The
condenser fan circulate surrounding air over the out-
side of the channels. The channels have fins designed
to improve the transfer of heat from the refrigerant gas
to the air. This removal of heat causes the refrigerant to
condense. Liquid refrigerant leaves the condenser and
flows through the condenser pressure control solenoid
(SV1) to the receiver.
The receiver stores the additional charge necessary for
low ambient operation. The receiver is equipped with a
fusible plug which melts on occurrence of very high
temperature to relieve the refrigerant pressure.
The refrigerant leaves the receiver and flows through
the liquid line service valve to the subcooler. The sub-
cooler occupies a portion of the main condensing coil
surface and gives off further heat to the passing air.
The refrigerant then flows through a filter-drier where a
screen and absorbent keep the refrigerant clean and
dry.
The refrigerant then flows through the liquid line sole-
noid valve (SV2) to the suction line heat exchanger.
Here the liquid is further reduced in temperature by giv-
ing off some of its heat to the suction gas.
The liquid then flows to the evaporator expansion valve
which reduces the pressure of the liquid and meters
the flow of liquid refrigerant to the evaporator to obtain
maximum use of the evaporator heat transfer surface.
The refrigerant pressure drop caused by the expansion
valve is accompanied by a drop in temperature so the
low pressure, low temperature fluid that flows into the
evaporator tubes is colder 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 removed from the air circulated over
the evaporator. This cold air is circulated throughout
the refrigerated compartment to maintain the cargo at
the desired temperature.
The transfer of heat from the air to the low temperature
liquid refrigerant causes the liquid to vaporize.
This low temperature, low pressure vapor passes
through the compressor suction modulation valve
(CSMV) and heat exchanger and then returns to the
compressor. In the heat exchanger the refrigerant
absorbs more heat from the high pressure/high tem-
perature liquid.
The CSMV controls the compressor suction pressure
thereby matching the compressor capacity to the load.
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