TM 9-4120-402-14
Section III TECHNICAL PRINCIPLES OF OPERATION
1-11. REFRIGERATION CYCLE.
The following information describes the function of the components in this unit, listed in the order that the refrigerant
flows through the refrigeration system.
a. The COMPRESSOR (1) takes cold, low pressure refrigerant gas and compresses it to a high temperature, high
pressure gas. This gas flows through the metal tubing to the CONDENSER COIL (3A), SUBCOOLER (3B) and
RECEIVER (4).
b. The CONDENSER FAN (5) draws outside ambient air through the CONDENSER COIL (3A) and SUBCOOLER
(3B). The high temperature, high pressure gas from the COMPRESSOR (1) is cooled by the flow of air and condenses
to a high pressure liquid.
c. The REFRIGERANT DESICCANT DEHYDRATOR (filter-drier) (14) removes any moisture (water vapor) or dirt
that may be carried by the liquid refrigerant.
d. The SIGHT GLASS (8) indicates the presence of moisture and quantity of refrigerant in the system.
e. The EXPANSION VALVE (9) and DISTRIBUTOR (10) control the amount and pressure of liquid refrigerant to the
EVAPORATOR COIL (11). The EXPANSION VALVE (9) senses the temperature and pressure of the refrigerant as it
leaves the EVAPORATOR COIL(11). The valve constantly adjusts the flow of liquid refrigerant to the EVAPORATOR
COIL (11) depending on the heat load to the unit.
f. The liquid refrigerant leaves the EXPANSION VALVE (9) at a reduced pressure and enters the EVAPORATOR
COIL (11). The reduction in pressure and the warmer air being forced across the tubes of the coil cause the refrigerant to
evaporate.
The EVAPORATOR FAN (12) circulates the warm air from the conditioned space through the
EVAPORATOR COIL (11). The refrigerant absorbs heat when it changes from a liquid to a gas and is cooled.
g. To prevent compressor overload and damage during start-up, SOLENOID VALVE (2) opens when the compressor
is not running to equalize system pressure. This valve closes at start of cooling cycle.
h. The SERVICE VALVES (15) are provided for charging, and general servicing of the high and low pressure sides
of the refrigerant system.
i. The PRESSURE SWITCH (LOW) (7), the PRESSURE SWITCH (HIGH) (6) and the PRESSURE RELIEF VALVE
(13) are provided to protect the unit from damage due to pressure extremes.
j. The flexible METAL HOSE ASSEMBLY (DISCHARGE) (16) and METAL HOSE ASSEMBLY (SUCTION) (17)
provide vibration isolation between the compressor and other components of the refrigeration system.
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