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 TM 55-1905-220-14-8
4-29. AIR CONDITIONING SYSTEM - MAINTENANCE INSTRUCTIONS (Continued).
(1) Observe compressor operation for approximately five minutes. If there is not evidence of liquid
refrigerant return to compressor, open suction valve wide. If there is evidence of liquid returning to the
compressor, throttle suction valve until proper suction pressure is obtained. Liquid return to compressor will be
indicated by a sudden drop in suction temperature and rapid fluctuation in suction pressure. If these conditions
continue, or the compressor develops a knock, stop it immediately and shutoff liquid supply to evaporator.
After about five minutes, open liquid supply to evaporator and restart with suction valve throttled. When all
evidence of liquid return disappears, open suction valve wide.
(m) Check compressor oil pressure. Should be 45-55 psi (310.3 379.2 kPa) above suction pressure.
(n) Check operation of condenser water regulator. If it is operating properly, close condenser water
regulator bypass valve. Adjust water regulator to maintain a head pressure of 90 to 125 psig (620.5 to 861.9
kPa). If a water regulator is not provided, throttle water outlet valve to maintain required head pressure.
(3) Operating.
(a) A complete check should be made every hour of all temperatures, pressures, and the oil level in the
compressor crankcase.
(b) Avoid frost formation on compressor cylinders, suction lines and crankcase. This is caused by liquid
refrigerant returning to the compressor. If this condition persists, check expansion valves for proper operation.
Suction gas entering the compressor should be about 65 (18.30C) for air conditioning.
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(c) Adjust sea water flow through condenser to maintain a condensing refrigerant pressure not exceeding
125 psig (861.9 kPa).
(d) Compressor oil pressure not to exceed 45 55 psi (310.3 379.2 kPa) above suction pressure.
(e) The temperatures of the refrigerated spaces should be maintained as specified.
(f) If the compressor discharge gas temperature exceeds 240 (115.6 ), the heat interchanger should
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C
be bypassed by closing the liquid inlet valve and opening the bypass valve. The heat interchanger should
otherwise be kept in operation.
4-867
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