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 TM 55-1905-219-14-8
4-28.
AIR CONDITIONING SYSTEM-MAINTENANCE INSTRUCTIONS (Continued).
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
bull's-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.
4-832
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