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 TM 55-1905-219-14-8
4-28. AIR CONDITIONING SYSTEM - MAINTENANCE INSTRUCTIONS (Continued).
(6)
Refrigerant Undercharge.
(a) If the conditions listed below exist simultaneously, the system is short of refrigerant. Test for
leaks and repair any found. Add refrigerant to restore charge to correct level.
1
No liquid level in receiver.
2
Vapor bubbles in liquid line sight glass.
3
Compressor runs continuously or short cycles on low pres-
sure cut-out.
4
Low suction and head pressures.
5
Required temperatures in refrigerated spaces or other
medium being cooled cannot be maintained.
6
Hissing sound at control valves (caused by vapor in liquid
lines).
(7)
Refrigerant Overcharge.
If the system is overcharged with refrigerant, it will result in high head pressure. The condenser will be
flooded with liquid refrigerant and its capacity will be reduced. This may cause the compressor to short cycle
on high pressure cut-out and possibly cause damage to the compressor. System overcharge will also result in
high power consumption and, if an expansion valve is leaky, in increased flooding of refrigerant to the
compressor during the off cycle. If refrigerant overcharge is indicated, remove refrigerant to restore charge to
correct level.
(8)
Refrigerant Flooding.
Whenever a refrigeration system is started after a shutdown, liquid refrigerant may flood back to the
compressor. If an excessive amount of liquid refrigerant has been laying in the coils, it will overflow into the
suction line on start up. Avoid flooding by temporarily throttling the compressor suction stop valve. The
thermal expansion valves must not be reset to avoid flooding at this time or their performance will be faulty
during normal operation.
4-844
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