TM 9-4120-378-14
Section II. DIRECT SUPPORT MAINTENANCE PROCEDURES
REFRIGERATION SYSTEM.
Description.
5.3.1
Whenever it is necessary to open the refrigeration system for any reason, discharge
the refrigerant carefully. Avoid contact with liquid refrigerant. Severe freezing of
body tissues can take place with extreme rapidity. Avoid excessive inhalation of
refrigerant gas, and ventilate the area in which it is released. Refrigerant gas in con-
tact with flame or hot surfaces is converted to phosgene, a highly toxic gas having
an odor similar to newly mown grass or hay.
The refrigeration system, illustrated by the refrigerant flow diagram, is a mechanical, vapor-cycle circuit consist-
a.
ing of the evaporator, thermal expansion valve, compressor, condenser, and the necessary valves and cutout
devices for automatic control during operation.
b.
The thermal expansion valve releases high-pressure liquid refrigerant into the evaporator at reduced pressure.
The liquid refrigerant begins to vaporize by absorbing heat from the air passing over the outside surface of the
c.
evaporator coil.
The heated vapor is sucked out of the evaporator section by the compressor and is forced into the condenser sec-
d.
tion under high pressure where it is cooled and condensed back into a liquid.
The heat released during condensation is carried off by the condensing airstream.
e.
The liquid refrigerant flows from the condenser to a receiver to a subcooler and then to the thermal expansion
f.
valve to repeat the cycle.
If the temperature control switch (evaporator return-air thermostat) becomes satisfied or the evaporator return-air
g.
temperature is lower than the point at which you have set the control, the refrigeration system will switch to a
bypass condition.
The temperature control switch will activate the normally open liquid bypass solenoid valve and shut off the evap-
h.
orator section of the unit. You will notice that the compressor will continue to pump as usual, and the suction
pressure will begin to drop.
When the suction pressure reaches about 65 psig (4.6 kg/cm2), the valve starts to open in an effort to maintain
i.
the suction pressure above about 55 psig (3.86 kg/cm2).
As the suction temperature goes up, due to the opening of the pressure regulating valve, the quench expansion
j.
valve will start to meter liquid refrigerant into the suction line to maintain the suction temperature below 75 F
(24 C).
The action of the pressure regulating valve and quench valve is automatic. This action may also occur at extreme
k.
conditions in an attempt to maintain the suction pressure (even during the COOLING mode) at a point above 55
psig (3.86 kg/cm2) and the suction temperature (measured at the quench bulb well) below 75 F (24 C).
The condenser louvers are operated by a refrigerant-powered actuator located in the high-pressure part of the sys-
l.
tem. This actuator should be fully extended (louvers open) at approximately 80 F (27 C) at 260-220 psig
