(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.

 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH EFIS ú

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
 (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
 airflow passages and clean equipment and orifice if excessively
 contaminated, then install equipment.

Low shelf pressure, applicable plenum pressure OK.
 (a)  
Check shelf airflow orifices for proper configuration and for leakage through orifices which should be taped closed.

 (b)  
Check shelf to plenum opening and if obstructed remove obstruction.

 NOTE: To check for obstruction remove shelf to plenum
____ fasteners and pull apart only enough to observe opening. Obstruction here may or may not affect plenum pressure depending on the obstruction magnitude.
 (c)  
Check for excessive leakage where shelf mates to plenum.

 Repair if necessary.High plenum pressure.

 (a)  
Check for obstruction in shelf to plenum opening.

 (b)  
Check that orifice in plenum outlet duct is not missing, if missing install proper orifice. If not missing check for proper size and replace if necessary.

Any one plenum pressure low.

 (a)  
Check for obstruction to plenum outlet duct and remove if found. Check also that correct orifice is installed and replace if wrong size.

 (b)  
Check for excessive leakage where shelf mates to plenum and at

 duct to plenum connection. Repair as applicable.Instrument panel cooling tube pressure low (one side).

 (a)  
Straighten out kink in tube or remove obstruction from tube.

 NOTE: If low pressure is observed at all ports of one side
____ straighten out tube or remove obstruction from tube which draws air from that side.
All instrument panel cooling tubes pressure low.
 (a)  
Repair leaky duct joint or straighten out kink in main

 instrument cooling duct.One or more instrument panel or Flight Management Computer System CDU cooling tube pressure(s) high, other panel tube pressure(s) low.

 (a)  
Condition results from low tube pressure (Ref par. A.(7)).

 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH EFIS ú

 21-58-03
 ú ú 01 Page 105 ú Nov 15/98
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
　
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