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 TM 55-1905-220-14-8
4-29. AIR CONDITIONING SYSTEM - MAINTENANCE INSTRUCTIONS (Continued).
WARNING
Wear goggles to prevent liquid R-12 from getting into the eyes when charging, purging or opening the system
for repairs.
d. Safety Precautions.
(1) Operating.
(a) Inspect oil level in compressor crankcase periodically. The proper time to check oil level is
immediately after the compressor has been shut down following a long period of operation. The oil level should
also be checked before starting the compressor. The ideal oil level is from one-half to three-quarters up on the
bulls-eye sight glass. The minimum oil level is one-quarter up on the glass.
(b) Check compressor oil pressure periodically. It should be 45 55 psi (310.3 379.2 kPa) above suction
pressure.
(c) Never start a compressor without making sure that any shutoff valve between the compressor and
the condenser is open.
(d) Do not jack or turn the compressor by hand when power is on.
(e) Whenever the compressor motor is first started, the operator should stand by the switch and start the
motor in short intermittent spurts until it is certain that the compressor is operating properly. If possible, the
compressor should be turned over several times by hand, to clear the cylinders of any oil that may have
collected there during shipment or erection. When starting up the compressor, avoid rapid pumping down of
the low side pressure. The operator should also be certain that liquid refrigerant is not being returned to the
compressor. Liquid return will be indicated by the crankcase and cylinder being relatively cold, sweating or
frosted.
(f) In case of severe vibration or unusual noise, stop the unit and investigate.
(g) Do not attempt to add oil to compressor crankcase while compressor is in operation. Isolate and
pump down to slightly above atmospheric pressure in crankcase before removing filler plug.
(h) Never bridge an overload or any other protective device because it kicks out during operation. Find
the trouble and make the proper repairs.
4-862
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