Cooling cycle.

TM 5-4120-393-14

a. Cooling cycle. Unit operation with mode selector switch set to COOL and the TEMPerature control thermostat

set to DECREASE.

(1) Compressor (B1), condenser fans, and evaporator fans start

(2) To prevent compressor overload and damage during startup, solenoid valve (K4) is open prior to start of

cooling cycle to equalize pressure on both sides of the compressor.

(3) The compressor (B1) takes 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 (C) and receiver (R1).

(4) The condenser fans draw outside ambient air over and through the condenser coil (C). The high

temperature, high pressure gas from the compressor (B1) is cooled by the flow of air and is condensed into a high

pressure liquid.

(5) The refrigerant desiccant dehydrator (filter drier) (D) removes any moisture (water vapor) or dirt that may be

carried by the liquid refrigerant.

(6) The liquid indicator (sight glass) (G) indicates the presence of moisture and quantity of refrigerant in the

system.

(7) The solenoid valve (K3) is controlled by the TEMPerature control thermostat 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.

(8) The expansion valve (V5) controls the amount and pressure of liquid refrigerant to the evaporator coil (E).

The expansion valve (V5) senses the temperature and pressure of the refrigerant as it leaves the evaporator coil By use

of a sensing bulb and external equalizer line the valve constantly adjusts the flow of liquid refrigerant to the evaporator coil

(E). The expansion valve (V5) allows the high pressure liquid to expand into a cool low pressure liquid.

(9) As the liquid refrigerant leaves the expansion valve (V5) it passes through a distributor and enters the

evaporator coil (E). As the liquid enters the coil at a reduced pressure, the reduction in pressure and the warmer air being

forced across the tubes of the coil cause the refrigerant to boil and change to a gas (vapor). The evaporator fans circulate

the warm air from the conditioned space over and through the evaporator coil. Refrigerant 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 (E), the air is

cooled.

(10) The refrigerant gas is then drawn back to the compressor (B1) and the cycle is repeated.

b. Bypass cycle. This unit has a bypass cycle which allows cooling operation at low cooling loads without cycling

the compressor (B1) on and off. In bypass, the refrigerant is piped from the compressor discharge (high side) to the

suction (low side) of the compressor, bypassing the evaporator coil (E).

(1) When the TEMPerature control thermostat on the control panel senses that cooling conditions have

reached the set point, it closes the solenoid valve (K3) to shut off refrigerant flow to the evaporator coil (E).

(2) As the compressor suction pressure start to drop, the pressure regulating valve (V2) opens to allow flow of

hot gas from the compressor.

(3) The liquid quench expansion valve (V4) senses the temperature of the gas at the suction side of the

compressor. To prevent excessively hot gas from reaching the compressor, the liquid quench expansion valve (V4)

opens to allow liquid refrigerant to mix with the hot gas.

(4) The linear actuating cylinder (L1) automatically controls the condenser air discharge louver assemblies to

maintain an adequate discharge pressure.

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