TM 9-4120-399-14
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 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 module 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 starts 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 cylinders (L1 and L2) automatically control the condenser air
discharge louver assemblies to maintain an adequate discharge pressure.
(5) The service valves (V1) are provided for charging, and general servicing of the high
and low pressure sides of the refrigerant system.
(6) The low pressure switch (S6), the high pressure switch (S5), and the pressure relief
valve (V3) are provided to protect the unit from damage due to pressure extremes.
1-11. HEATING.
elements, located in front of the evaporator coil, are energized. These elements are protected
from overheating by a thermal cutout switch. Three of the elements are thermostatically
controlled by the temperature control thermostat, and remaining three are on all of the time.
b. LO HEAT mode. When the mode selector switch is set for LO HEAT, only the three
thermostatically controlled heating elements are used.
