HEATING - 506780022

TM 5-4120-359-14

As the liquid refrigerant leaves the expansion valve (6) it passes thru the distributor (7) and enters the

evaporator coil (8). 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 blower

circulates 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 evaporator coil (8), the air is

cooled.

To prevent compressor overload and damage during startup, solenoid valve (17) is open at start of cooling

cycle to equalize pressure on both sides of the compressor.

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

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

the compressor, bypassing the evaporator coil (8).

When the temperature selector on the control panel senses that cooling conditions have reached the set

point, it closes the solenoid valve( 9) to shut off refrigerant flow to the evaporator coil (8).

As the compressor suction pressure starts to drop, the discharge bypass valve (14) opens to allow flow of hot

gas from the compressor.

The liquid quench expansion valve (15) 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 (15) opens

to allow liquid refrigerant to mix with the hot gas.

The linear actuating cylinder assembly (16) automatically controls the condenser discharge louver assembly

to maintain an adequate discharge pressure.

The service valves (10) are provided for charging, and general servicing of the high and low pressure sides of

the refrigerant system.

The low pressure switch (11), the high pressure switch (12) and the pressure relief valve (13) are provided to

protect the unit from damage due to pressure extremes.

1-12. HEATING

When the MODE SELECTOR SWITCH is set for HIGH HEAT, heating elements, located behind the evaporator coil, are

energized. These elements are protected from overheating by a thermal cutout switch. Nine of the elements are

thermostatically controlled by the TEMPERATURE CONTROL, and remaining six are on all of the time. When set for

LOW HEAT, only the thermostatically controlled elements are energized.

1-7 (1-8 blank)