ARMY TM 9-4120-380-14
AIR FORCE TO 35E9-136-21
The primary expansion valve (VS) controls the amount and pressure of liquid refrigerant to the evaporator coil (E).
By use of a sensing bulb and external equalizer line, the primary expansion valve (V5) senses the temperature
and pressure of the refrigerant as it leaves the evaporator coil (E) and constantly adjusts the flow of liquid
As the liquid refrigerant leaves the expansion valve (V5), it passes through a distributor (D) and enters the
evaporator coil (E). The evaporator fan (B1) circulates warm air from the conditioned space over and through the
evaporator coil (E). As the liquid refrigerant enters the coil at reduced pressure, the combination of pressure
reduction and warmer air being forced across the tubes of the coil causes the refrigerant to boil and change from a
liquid to a gas Refrigerant 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.
After the low pressure refrigerant gas passes through the evaporator coil (E), the gas then flows through the other
half of the heat exchanger (H) where is it superheated by the high pressure liquid refrigerant leaving the
condenser coil (C).
The superheated refrigerant gas flows through a refrigerant strainer (F2) to remove any particles from the gas
before it flows into the compressor (B2).
The refrigerant gas is then drawn back to the compressor (B2) and the cycle is repeated.
A service valve (V1) allows the condenser fan damper actuator (A) to be isolated from the refrigerant lines during
maintenance. A second service valve (V2) located between the receiver (R) and the heat exchanger (H) isolates
the refrigeration system low side from the high side during pump down.
Service valves (V3, V7) can be used to isolate the liquid quench and hot gas bypass systems during pump down
or for maintenance purposes.
Discharge service valve (V9) and suction service valve (V8) are provided for isolation of the compressor (B2)
during maintenance or replacement procedures.
The high refrigerant pressure switch (S5) and low refrigerant pressure switch (S4) are provided to protect the
compressor (132) from damage due to pressure extremes.
Vibration eliminators (VE1, VE2) are installed in the compressor (B2) suction and discharge lines to isolate
compressor vibration from the other refrigerant piping.
1.14.2 Bypass Cycle. The air conditioner has a bypass cycle which allows the cooling operation during low cooling
loads without cycling the compressor (B2) on and off In the bypass cycle, the refrigerant is routed from the compressor
discharge (high) side to the suction (low) side of the compressor, bypassing the evaporator coil (E).
During low load cooling conditions, excess cooling capacity causes a reduction in suction line pressure. This low
pressure condition is caused by closing of the solenoid valve (L1)
The low cooling load produces decreasing return air temperature, causing the thermostat to open solenoid valve
(L2). As the compressor suction pressure starts to drop, the hot gas bypass valve (V4) opens to allow flow of hot
gas to the suction line between the evaporator coil (E) and heat exchanger (H).
The liquid quench expansion valve (V6) senses the temperature of the hot gas being bypassed through the hot
gas bypass valve (V4) to the suction line. To prevent excessively hot gas from reaching the compressor, the
liquid quench expansion valve (V6) opens, when necessary, to allow liquid refrigerant to mix with the hot gas.
1.14.3 Venting Cycle. Recirculated air flow can be provided by the air conditioner when the MODE SELECT switch is
set to VENT. The evaporator fan (B 1) is turned on, and the compressor (B2) and condenser fan (B3) remain off.
1.14.4 Heating Cycle
. When the MODE SELECT switch
on the control panel
to either AUTO
or HEAT, the
electric heating elements in front of evaporator coil (E) are capable of being energized Operation of the heating is
controlled by two stages of the 4-stage thermostat, located in the return air filter section of the air conditioner. The
thermostat automatically switches m three or six of the electric heating elements, depending on return air temperature
and thermostat setting