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A737-300/400/500MAINTENANCE MANUAL
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F. Trouble Shooting Charts
(1)  The following chart is for normal blower operation, ie 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.

OFF LIGHT DOES NOT ILLUMINATE IMMEDIATELY - Accomplish equipment cooling system performance test and correct condition as identified in fault isolation procedure.
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.

 (2)  
Low plenum pressures (ALL).

 NOTE: For this condition to occur low pressures would likely be
____ observed at all test ports although a few of the shelf test ports may possibly be within tolerance.
 (a)  
Check the entire duct system for joint leakage. Do not overlook P6 panel, main instrument panel or P9 panel ducts.

 (b)  
Check that alternate blower check valve is installed and functions properly.

 NOTE: If alternate blower check valve sticks in open position,
____ there will be low airflow from the equipment cooling exhaust port.
 (c)  Check for obstruction in exhaust ducts.
 NOTE: A reduction of airflow from exhaust port would probably
____ accompany this problem.
 (d)  
Check for general system contamination. If signs of contamination are observed remove and clean blower and where applicable, clean equipment rack shelves and plenum outlet duct orifices.

 (e)  
If, after accomplishing (all above steps) all plenum pressures are still low, replace blower.

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 (3)

(4)

(5)

(6)

(7)

(8)

(9)

A
737-300/400/500MAINTENANCE MANUAL
High shelf pressure.
 (a)  Check applicable equipment rack shelf for unauthorized tape,
 contaminants or foreign material obstructing shelf orifices.
 Remove material and/or clean as required.
 NOTE:____ Metalized tape is properly used to close some of the
 orifices.  Check proper engineering drawing before
 removing any tape.
 (b)  Remove any draw through equipment from applicable shelf and
 remove any obstruction to orifice found.
 (c)  Remove any obstruction found in draw through cooled equipment
　
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