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TM 5-4120-287-15
(h) Condenser-subcooler Assembly.
(1) Condenser subassembly. The condenser (fig. 1-4) is a crossflow-type heat exchanger of copper tube and
aluminum fin construction. The condenser rejects the heat absorbed by the refrigerant in the evaporator and the heat of
compression added by the compressor; thereby transforming the refrigerant vapor into a liquid. The liquid refrigerant is
then passed from the condenser outlet to the receiver inlet.
(2) Subcooler subbassembly. The subcooler (fig. 1-4) is integral with the condenser, and is cooled by air drawn across
it by the condenser fan. The subcooler, located in the line between the receiver and the filter drier, lowers the refrigerant
temperature approximately 80F; and thereby prevents flashback (vaporization) of the liquid refrigerant before it passes
through the expansion valve.
i. Low Ambient Switch. The low ambient temperature switch (fig. 6-2) located in the condenser air inlet stream closes
when the ambient air temperature falls below 400F; causing the cooling cycle to cease by de-energizing the motor
compressor and condenser fan motor. The evaporator fan motor continues to operate, recirculating the shelter air and/or
drawing in fresh air. When ambient temperature rises above 50F, the low ambient temperature switch opens; then upon
pressing the system reset switch, the cooling cycle resumes.
j. Receiver. The receiver, located between the condenser and the subcooler (fig. 1-4), stores condensed (liquified)
refrigerant. This stored liquid refrigerant acts as a seal between the partial vapor-liquid state in the condenser and the
liquid supply to the evaporator expansion valve.
k. Hot Gas Bypass Valve. The hot gas bypass valve (fig. 1-4) regulates the compressor inlet pressure. It consists of
a housing with a replaceable power unit. The power unit contains a spring and diaphragm which actuate the valve
mechanism. Three tube connections on the housing accommodate the inlet and outlet lines and the pressure equalizing
line which is connected to the compressor inlet line. The valve maintains a minimum compressor inlet pressure of 28 psig
during light-load operation; thus preventing evaporator air side freeze-up. This function is accomplished by passing
compressor discharge gas into the compressor inlet line.
l.
Filter-drier. The filter-drier (fig. 1-4) consists of a sheet of metal housing with ½-inch flared inlet and outlet
connections. The unit contains a conical filter screen, the base of which is mounted to a fiber glass pad at the outlet end
of the housing. Within the housing, both inside and outside the cone screen, is the drying agent (desiccant), which is cast
in the form of 1/8-inch balls of activated aluminum. (The filter-drier is installed directly in the liquid-refrigerant line between
the subcooler subassembly and the refrigerant solenoid valve.) It is used to remove entrained moisture, sludge, dirt, and
other foreign particles from the liquid refrigerant. The filter-drier is a throwaway unit which must be replaced when the
refrigerant charge is replaced and/or when the system has been subjected to extensive maintenance or servicing.
m. Solenoid Valve. The solenoid valve (fig. 1-4) is an electrically operated, thermostatically controlled shutoff valve
located in the liquid refrigerant line between the filter-drier and the expansion valve. When the solenoid valve is closed,
refrigerant flow to the expansion valve is stopped and compressor discharge has is bypassed to the compressor suction
inlet line through the hot gas bypass valve. When the air conditioner is operating in the cooling mode the compressor
operates continuously. Air temperature regulation is accomplished by the thermostatically controlled opening and closing
of the solenoid valve.
n. Refrigerant Liquid Sight Indicator. The refrigerant liquid sight indicator (fig. 1-2), installed upstream of the
expansion valve, can be viewed through a port in the air conditioner rear wall. The indicator consists of a metal body with
½-inch inlet and outlet connections; and a glass viewing window, permitting visual indication of adequate liquid refrigerant
flow to the thermostatic expansion valve. The system moisture content indicator,
1-3
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