TM 9-4120-385-14
(4) The drier/filter dehydrator (D) removes any moisture (water vapor) or dirt that
may be carried by the liquid refrigerant.
(5) The solenoid valve (L1) is controlled by the temperature control knob 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.
(6) 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. Because of the sensing bulb and "external equalizer
line" the valve constantly adjusts the flow of liquid refrigerant to the evaporator coil (E).
(7) As the high pressure liquid refrigerant leaves the expansion valve (V5), it enters
the evaporator coil (E). 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 impeller circulates the return 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 space comes in contact with the
evaporator coil (E), the air is cooled.
(8) To prevent compressor damage during startup, the solenoid valve (L2) is normally
open 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 (E).
(1) When the temperature selector on the control panel senses that cooling conditions
have reached the set point, it closes the solenoid valve (L2) to shut off refrigerant flow to the
evaporator coil (E).
(2) As the compressor suction pressure starts to drop, the pressure regulator (V2)
opens to allow flow of hot gas from the compressor.
(3) The quench 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 quench valve
(V4) opens to allow liquid refrigerant to mix with the hot gas.
1 1 3 . HEATING
When the mode selector is set for HI-HEAT, six heating elements, located behind the
evaporator coil, are energized. These elements are protected from overheating by a thermal
cutout switch. Three of the elements are controlled by the temperature selector, and the
remaining three are on all of the time. When set for LOHEAT, only the three thermostatically
controlled elements are energized.
1-11/(1-12 blank)
