Type: 737-700 Discrepancy: PACK TRIP OFF light on at higher ambient tempertures
during ground operation and stays off after reset.
Possible Fix: Fan bypass check valve, part # 5848999-1
Tip: And indication of this fault would be little or no airflow from the Ram
air exhaust duct outlet. Like a classic with the pack operating, place your
hand in front of the Ram inlet, check draw on your hand and compare to the
other pack. The same is true of the exhaust.
You can put your hand up the pack exhaust and feel the check valve. Removing
the aft access panel on the Plenum/Diffuser assy, gives you great access to
the fan bypass check valve to inspect it or replace it.
Reason/explanation: On the ground the heat exchangers need the check valve
closed to create a low pressure zone that pulls air through the diffuser and
out the ram air exhaust. Then the impeller fan sends the air through the
diffuser and out the ram exhaust. The operation of this
plenum/impeller/diffuser/check valve network, performs the same function as
the turbo fan on the 300/500’s
Applicable reference: AMM 21-50-00-003, 21-50-00-014, FIMM 21-52-818 task 818
Thanks to Tom S. for his input !