Section III. PRINCIPLES OF OPERATION

TM5-4120-347-14

Section Ill.

PRINCIPLES OF OPERATION

See figure 1-3.

REFRIGERATION CYCLE

1-8.

a. Cooling Cycle

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 split condenser coil (3) and receiver (4).

The condenser fan draws outside ambient air over and through the two section condenser coil (3).

The high temperature, high pressure gas from the compressor (1) 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 quantity of refrigerant in the system.

The refrigerant desiccant dehydrator (filter drier) (6) removes any moisture (water vapor) or dirt that

may be carried by the liquid refrigerant.

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

(9). The expansion valve (8) senses the temperature and pressure of the refrigerant as it leaves the evaporator

coil. By use of the sensing bulb in the bulb well (10) and "external equalizer line" the valve constantly adjusts

the flow of liquid refrigerant to the evaporator coil (9).

As the liquid refrigerant leaves the expansion valve (8) it enters the evaporator coil (9). 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 or "flash" 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 evaporator coil (9), the air is

cooled.

To prevent compressor overload and damage during start up, solenoid valve (16) is open at start of

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

b. 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 compressor, bypassing the evaporator coil (9).

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 (9).

As the compressor suction pressure starts to drop, the pressure regulator (11) opens to allow flow of

hot gas from the compressor.

The quench valve (17) senses the temperature of the gas at the suction side of the compressor. To

prevent excessively hot gas from reaching the compressor the quench valve (17) opens to allow liquid

refrigerant to mix with the hot gas.

The linear actuating cylinder assembly (15) automatically controls the condenser discharge louver

assembly.

The service valves (12) are provided for charging, and general servicing of the high and low pressure

sides of the refrigerant system.