ARMY TM 9-4120-380-14
AIR FORCE TO 35E9-136-21
Section III. TECHNICAL PRINCIPLES OF OPERATION
. This section tells how the air conditioner works
in its different cycles (see fig. 1-3).
. The air conditioner provides automatic and manual cooling and heating
modes, and a manual venting mode when the control panel PRIMARY/BACK-UP switch is set to PRIMARY. When the
switch is set to BACK-UP and the POWER ON light is on, the air conditioner can start operating immediately in the
selected mode of operation.
OPERATING CYCLE. Normal operation of this air conditioner is in AUTO (automatic) mode, which provides
supply air cooling or heating temperature regulation as required to maintain a pre-set value. This temperature regulation
is accomplished by cooling, bypass and heating cycles. A manually selected venting or recalculating ambient
compartment air flow cycle is also available for use These cycles are described in the following paragraphs.
1.14.1 Cooling Cycle
. Air conditioner operation when cooling
starts about 5 seconds after the compressor (B2).
The compressor (B2) receives low pressure superheated refrigerant gas and compresses it to a high pressure,
high temperature gas. This gas flows through metal tubing to the condenser coil (C).
The condenser fan (B3) draws outside ambient air over and through the condenser coil (C). The high pressure,
high temperature gas from the compressor (B2) is cooled by the flow of air and condensed into a high pressure
liquid If ambient air temperature increases, the gas entering the condenser coil (C) will increase m pressure,
causing the condenser fan damper actuator (A) to open the damper and allow an increased flow of air across the
condenser coil (C).
The receiver (R) stores excess refrigerant during periods of decreased load or low ambient temperature, or
during maintenance pump down procedures.
The high pressure liquid from the condenser is subcooled by the tube-in tube heat exchanger (H), which at the
same time superheats the low pressure refrigerant gas returning to the compressor (B2).
The drier filter (F1) removes any moisture (water vapor) or dirt that may be carried by the liquid refrigerant
leaving the heat exchanger (H).
The sight glass (G) indicates the quantity of refrigerant in the system.
The solenoid valve (L1) is used to control refrigerant flow to the primary expansion valve (VS5). The solenoid
valve (L1) is cycled open and closed by the thermostat located in the return air filter section of the air conditioner.
The thermostat also opens and closes solenoid valve (L2) during the bypass cycle.