99
Internal Pressure Relief Valves
Certain air conditioning compressors in the AJ, AW, AH, AV, AG, and SF families are quipped with a
unique internal pressure relief (IPR) valve. It prevents abnormally high head pressures from devel-
oping if a condenser fan motor fails or air passages in the condenser coil become blocked by dirt,
leaves, paper, etc. The IPR valve relieves pressure from the high pressure side to the low pressure
side of the system. It does not relieve pressure from the system to the atmosphere. See Table 6-2.
Compressors with IPR valves are frequently used in air conditioning and heat pump systems, and
occasionally used in refrigeration systems. The IPR valve may also open to relieve hydraulic pres-
sures in the event of slugging. This is apt to occur on startup if refrigerant has been allowed to mi-
grate to the compressor crankcase. It is a characteristic of the IPR valve that once it has “popped,”
it will not reset until the compressor has been stopped and the pressure allowed to equalize.
If a high to low side leak within the compressor is suspected, stop the system, equalize the pres-
sures, permit the IPR valve to close, and restart the compressor to double check before deciding
to change the compressor.
Table 6-2: Compressors with IPR valves
AG Models AHA7513Z SFA5560E
AV Models AHA7515J SFA5572E
AW Models AHA7521Z SFA5581E
AHA4520E AHA7524J SFAA530Z
AHA4522E AJC5519E SFAA536Z
AHA4524E AJD8520E SFAA540Z
AHA4531E SFA5554E
AHA4540E SFA5558E
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