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 TM 55-1905-219-14-8
4-28.
AIR CONDITIONING SYSTEM-MAINTENANCE INSTRUCTIONS (Continued).
(23)
Safety Devices.
(a) Each compressor is equipped with high and low pressure control switches, an oil pressure safety
switch and a pressure relief valve. The functions of the high and low pressure control switches and the oil
pressure safety switch have been described above. Refer to paragraphs 4-28a(13) and 4-28a(19).
(b) The compressor relief valve is connected between the high and low pressure sides of the
system and allows excessive head pressure to relieve back to the suction or low pressure side of the
compressor. The compressor is equipped with an external relief valve set at 225 psi (1551.4 kPa). If the high
side pressure rises to exceed the low side pressure by the relief valve setting, the relief valve opens and
permits refrigerant gas to discharge from the high to the low pressure side of the system.
(c) A relief valve set at 225 psi (1551.4 kPa) is also installed in the equalizing line connecting the
condenser and receiver. This valve will relieve excessive pressure which might build up in a full receiver
during shutdown when the stop valves are closed. If the pressure in the receiver should rise above 225 psi
(1551.4 kPa), the relief valve will open and allow refrigerant to flow into the condenser.
(d) Another relief valve, also set at 225 psi (5151.4 kPa), is installed in a line connecting the
refrigerant side of the condenser to the overboard discharge. This valve will protect the system should
refrigerant pressure ever be greatly increased by very high temperatures, such as during a fire.
4-824
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