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TM 9-4120-367-14
TM 07592B-14/1
Section Ill. PRINCIPLES OF OPERATION
1.11 REFRIGERATION CYCLE.
1.11.1
The Refrigerant Cycle. The refrigeration system removes heat from a given area. See figure 1-5. for a schemat-
ic of the refrigeration cycle.
a.
b.
c.
d.
e.
f.
g.
h.
i.
The compressor (1A) takes cold, low pressure refrigerant gas and compresses it to a high temperature, high pres-
sure gas. This gas flows thIOUgh the metal tubing to the split condenser coil (3A) and receiver (4).
The condenser fan draws outside ambient air over and through the two section condenser coil (3A). The high tem-
perature, high pressure gas from the compressor (1A) is cooled by the flow of air and is changed into a high
pressure liquid.
The liquid sight glass (5) indicates the presence of moisture and the quantity of refrigerant in the system.
The drier/filter dehydrator (6) removes any moisture (water vapor) or dirt that may be carried by the liquid refrig-
erant.
The solenoid valve (7) is controlled by the temperature selector on the control panel. This valve will shut off the
flow of refrigerant to the evaporator section when the temperature in the conditioned area reaches the set point.
The expansion valve (8) controls the amount and pressure of liquid refrigerant to the evaporator coil (10). The
expansion valve (8) senses the temperature and pressure of the refrigerant as it leaves the evaporator coil. By use
of the feeler bulb in the bulb well (11) and ’’external equalizer line,’’ the valve constantly adjusts the flow of liquid
refrigerant to the evaporator coil (10).
As the high pressure liquid refrigerant leaves the expansion valve (8), it enters the evaperator coil (10). As the
liquid enters the coil, due to the size difference between the coil and the tubing, the pressure is suddenly decreased.
As the pressure decreases, the liquid refrigerant “flashes” to a gas. The evaporator blower circulates the warm
air from the conditioned space over and through the evaporator coil. Liquid absorbs heat when it changes from
a liquid to a gas. As the air from the conditioned spaces comes in contact with the evaporator coil (10), the air
is cooled.
The accumulator (12) holds any liquid refrigerant which did not change to a gas in the evaporator. Heat in the
evaporator section will boil this liquid to a gas before entering the compressor.
To prevent compresser damage during start-up, the solenoid valve (19) is normally open to equalize pressure on
both sides of the compressor.
1.11.2 Bypass System. This unit has a bypass system which allows cooling operation at low cooling loads without
cycling the compressor on and off. In bypass, the refrigerant is piped from the discharge to the suction side of the com-
pressor, bypassing the evaporator coil (10).
a. When the temperature selector on the control panel senses that cooling conditions have reached the set point, it
closes the solenoid valve (7) to shut off refrigerant flow to the evaporator coil (10).
b. As the compressor suction pressure starts to drop, the pressure regulators (20) open to allow flow of hot gas from
the compressor.
c. The quench valve (18) senses the temperature of the gas at the suction side of the compressor. To prevent exces-
sively hot gas from reaching the compressor, the quench valve (18) opens to allow liquid refrigerant to mix with
the hot gas.
1-12
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