TM 9-4120-407-14
SECTION III TECHNICAL PRINCIPLES OF OPERATION
1-12. REFRIGERATION CYCLE. The following information describes the function of the components in
this air conditioner, listed in the order that the refrigerant flows through the refrigeration systems.
Reference find numbers to Figure 1-2 Refrigeration Schematic.
a . The Compressor. The Compressor (1) takes cold, low pressure refrigerant gas and compresses it to a
high temperature, high pressure gas. This gas flows through the metal tubing passing through the Service
Valve (2) and the High Pressure Cutout Switch (3) to the Condenser Coil (4) and Receiver (9).
b. The Solenoid Valve. The Solenoid Valve (5) prevents compressor overload and damage during start-up
by remaining open when the compressor is not running to equalize the pressure. This valve closes at start of
cooling cycle.
c. The Condenser Fan. The Condenser Fan (6) draws outside ambient air through the Condenser Coil (4).
The high pressure, high temperature gas is cooled by the flow of air and is condensed to a high pressure
liquid.
d. The Pressure Relief Value. The Pressure Relief Valve (7) provides protection for the compressor due to
extreme pressures.
e. The Linear Actuator. The Linear Actuator (8) is activated by pressure in the cylinder and allows more
air to flow to the condenser coil.
f. The Dehydrator. The Dehydrator (10) removes moisture (water vapor) or dirt that may be carried by
the liquid refrigerant.
g. The Liquid Sight Indicator. The Liquid Sight Indicator (11) indicates the presence of moisture and
quantity of refrigerant in the system.
h . The Expansion Valve. The Expansion Valve (12) controls the amount and pressure of liquid refrigerant
to the Evaporator Coil (13). This valve senses temperature and pressure of the refrigerant as it leaves the
evaporator coil and adjusts the flow of liquid refrigerant to the evaporator coil depending on the heat load
to the air conditioner. The liquid refrigerant leaves the Expansion Valve (12) at a reduced pressure and
enters the Evaporator Coil (13). The reduction in pressure and the warmer air being forced across the tubes
of the coil cause the refrigerant to evaporate.
i. The Evaporator Fan. The Evaporator Fan (14) draws the warm air from the conditioned space and
blows it through the Evaporator Coil (13). The refrigerant absorbs heat when it changes from a liquid to a
gas and the air passing over the coil is cooled.
j. The Service Value. The Service Valve (15) is provided for charging and general servicing of the high
and low pressure sides of the refrigerant system.
k. The Low Pressure Cutout Switch. The Low Pressure Cutout Switch (16) protects the air conditioner from
damage due to pressure extremes,
1-13. HEATING. When the MODE Selector Rotary Switch is
set for HEAT, all heating
elements located
behind the evaporator coil are energized. These elements are controlled by the Temperature Control
Potentiometer. They are protected from overheating by thermal cutout switch.
1-8