THEORY OF OPERATION, COOLING AND HEATING

TM 9-4120-428-14

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OPERATOR'S, UNIT, DIRECT SUPPORT, AND GENERAL SUPPORT MAINTENANCE

AIR CONDITIONER, HORIZONTAL, COMPACT

(NSN 4120-01-502-1319)

THEORY OF OPERATION, COOLING AND HEATING

COOLING

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) and (3B) and RECEIVER (4).

The condenser fan draws outside ambient air over and through the two section CONDENSER COIL (3A) and (3B). 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 DEHYDRATOR, DESICCANT, REFRIGERANT (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, 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 air from the conditioned spaces comes in

contact with the EVAPORATOR COIL (9), the air is cooled.

To prevent compressor overload and damage during start-up, pressure equalizing SOLENOID VALVE (15) is closed at start

of cooling cycle. This valve opens when compressor is not running to equalize pressure on both sides of 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 module 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 s tarts to drop, the PRESSURE REGULATOR (10) opens to allow flow of hot gas

from the compressor. The QUENCH VALVE (16) 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 (16) opens to allow liquid refrigerant to

mix with the hot gas.

The LINEAR ACTUATING CYLINDER ASSEMBLY (14) automatically controls the condenser discharge louver

assembly.

The SERVICE VALVES (11) are provided for charging, and general servicing of the high and low- pressure sides of the

refrigerant system.

The LOW PRESSURE SWITCH (17), the HIGH PRESSURE SWITCH (13) and the PRESSURE RELIEF VALVE (12) are

provided to protect the unit from damage due to pressure extremes.

The flexible METAL HOSE ASSEMBLIES (2) and (18) provide vibration isolation between the compressor and other

components of the refrigeration system.

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