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 TM 55-1905-219-14-8
4-28. AIR CONDITIONING SYSTEM - MAINTENANCE INSTRUCTIONS (Continued).
(5)
Pumping Down.
If the system is to be opened for inspection or service, or is to be secured for an extended period (a
month or more), the system should first be pumped down. The system should never be opened while under a
vacuum to avoid harmful admission of air and moisture. Proceed as outlined below for the condensing unit.
NOTE
If compressor only is to be opened for service or repair, it is not necessary to
pump down entire system. To pump down compressor only, gradually close
suction stop valve while unit is operating. Run compressor (refer to step (b)
below) until suction pressure remains at 2 psig (13.8 kPa). Then stop the unit
and close discharge stop valve.
(a)
Close main liquid line stop valve (dryer bypass or inlet valve).
(b) Run compressor with compressor motor controller in AUTO position or L.P.BYPASS button
held in. Run compressor until a suction pressure of 2 - 3 psig (13.8 - 20.7 kPa) is obtained. Stop the unit.
After a few minutes, suction pressure may rise gradually. If this happens, restart unit and pump down again.
Repeat this operation until suction pressure remains at 2 psig (13.8 kPa). If compressor pounds or knocks
while pumping down, stop it for a few minutes, then restart.
(c)
Close compressor suction and discharge stop valves.
CAUTION
If compressor is to be shut down for an extended period, tag starting switch and
compressor stop valves. If compressor is started with discharge valve closed it
may be seriously damaged.
(d)
Secure sea water circulating system to condenser.
(e) For an extended shutdown, or if there is danger of water freezing in condenser tubes, open
vents top and drains at bottom of water heads and drain condenser.
4-839
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