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 TM 55-1905-219-14-8
4-28. AIR CONDITIONING SYSTEM - MAINTENANCE INSTRUCTIONS (Continued).
below 105F (40.6 )) may indicate liquid refrigerant return to compressor or excessive oil circulatin in system.
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Refer to Volume 3. Take corrective action promptly if crankcase temperature is abnormal.
(b) Discharge Temperature.
With the compressor warmed up and operating normally, the discharge gas temperature should not
exceed 240F (115.6 ). If it should, bypass the heat interchanger.
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(c) Head and Back Pressure.
Head and back pressures are basic indicators of system operation. Refer to Volume 3. Head and back
pressures will also show whether the compressor suction and discharge valves are operating correctly. If
suction pressure is abnormally high and discharge pressure abnormally low, either the suction or discharge
valves may be leaking. Leaky valves will usually result in lack of refrigeration and long running time.
(3) Compressor Noises.
(a) Compressor noises may be due to vibration because of improper mounting, or improperly aligned,
loose or worn compressor drive. These and other possible sources of compressor noises are listed with
corresponding remedies in Volume 3.
(b) In some cases, noise may seem to come from the compressor but originate elsewhere in the
system. Other possible sources of system noises are given in Volume 3.
(c) When investigating noisy operation, keep in mind that the operation of the capacity control system
will change the characteristic operating sound level of the compressor.
(4) Adjustment of Belt Drives.
(a) After a period of operation, new V-belts will stretch and slip if not kept tight. If the flywheel or motor
pulley appears to be warm, the belts are probably slipping. Slippage will cause loss of speed to the compressor
and excessive belt wear. Keep all belts at proper tension or they will soon be ruined.
(b) Belts can be adjusted by moving the universal adjustable motor rails. V-belts when properly
adjusted can be depressed about 1/2 to 3/4 inch (1.27 to 1.9 cm) with the pressure of one finger. Do not tighten
belts too much. Very tight belts will cause excessive wear of both the belts and main bearings of the motor and
compressor. In extreme cases, tight belts may cause shaft seal leaks.
(c) Fan belts should be checked and adjusted for proper tension in the same manner as above.
4-873
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