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A
737-300/400/500MAINTENANCE MANUAL
E. Few components of the equipment cooling exhaust system could cause failure of air movement in the system. The following trouble shooting charts are provided to isolate faulty components of the control and indicating system. If after using the trouble shooting charts the problem is not corrected, the trouble may be in the electrical wiring or loose and broken ducting. Refer to wiring diagram.
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A737-300/400/500MAINTENANCE MANUAL
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
F. Troubleshooting Charts
(1) The following chart is for normal blower operation; i.e., with blower selector switch at NORMAL. If problem was encountered with switch at ALTERNATE, substitute alternate blower and alternate blower relay and reverse check valves postions where applicable. For switch continuity in alternate position, check between contacts 4 and 5.
With electrical power provided, all equipment cooling system circuit breakers closed and position switch at NORMAL, EQUIP COOLING OFF light illuminates -Check operation of normal blower. IF -
blower electrical connector and check for voltage to connector. IF -BLOWER NOT OPERATING - Remove the normal
NO VOLTAGE - Check for continuity switch. IF -between contacts 2 and 3 of position
NO CONTINUITY - Replace the position switch.
VOLTAGE - Replace the normal blower
(AMM 21-58-12/401).
BLOWER IS OPERATING - Check that the automatic flow control valve is open. IF -
VALVE IS OPEN - Check that the normal blower check valve is open and that the alternate blower check valve is closed. IF -
BOTH CHECK VALVE POSITIONS OK - Remove the electrical connector from the low flow sensor (AMM 21-58-43/401 for effectivity).
EQUIPMENT COOLING OFF LIGHT REMAINS ON - Replace the equipment cooling low flow indicator relay, R438.
VALVE IS NOT OPEN - Replace the auto-matic flow control valve (AMM 21-58-31/401).
CONTINUITY - Replace the normal blower
relay, R29. EITHER CHECK VALVE POSITION NOT OK -Replace the applicable check valve (AMM 21-58-51/401).
EQUIPMENT COOLING LIGHT GOES OFF -Replace the low flow sensor (AMM 21-58-43/401).
Equipment Cooling Troubleshooting Charts Figure 101
A 737-300/400/500MAINTENANCE MANUAL
2. Equipment Cooling System Performance Trouble Shooting
_____________________________________________________
A. Fault Isolation
(1)
General
(a)
The following procedure should isolate faults in the equipment cooling system which cause low pressure readings noted in the system performance test. Since airflow for each item of equipment is affected by airflow throughout the system it is possible that correcting airflow at one location in the system may reveal another problem area which did not show up in the preceding test. After faults have been located and corrected, the system performance test must be rerun to assure a trouble free cooling system.
(b)
It would be unusual to find an equipment cooling system suffering from all the faults covered, therefore test data should be analyzed for type of fault before accomplishing fault isolation procedure. If all plenum pressures are low, retest system before proceeding for any other fault.
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