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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
 S 865-002
 WARNING: YOU MUST REMOVE THE PRESSURE FROM THE PNEUMATIC DUCTS BEFORE
_______ YOU REMOVE A PNEUMATIC SYSTEM COMPONENT. IF YOU DO NOT REMOVE THE PRESSURE FROM THE PNEUMATIC DUCTS, HOT HIGH PRESSURE AIR CAN CAUSE INJURIES TO PERSONS OR DAMAGE TO EQUIPMENT.
 (1) Remove the pressure from the pneumatic system (AMM 36-05-00/201).
 S 045-003
 WARNING: DO THE DEACTIVATION PROCEDURE TO PREVENT THE OPERATION OF THE
_______ THRUST REVERSER. THE ACCIDENTAL OPERATION OF THE THRUST REVERSER CAN CAUSE INJURIES TO PERSONS AND DAMAGE TO EQUIPMENT.
 (2)  
Do the deactivation procedure for the thrust reverser for the ground maintenance (AMM 78-31-00/201).

 S 015-004

 (3)  
Open the fan cowl panels (AMM 71-11-02/201).

 S 015-005
 WARNING: OBEY THE INSTRUCTIONS IN THE PROCEDURE TO OPEN THE THRUST
_______ REVERSERS. IF YOU DO NOT OBEY THE INSTRUCTIONS, INJURIES TO PERSONS AND DAMAGE TO EQUIPMENT CAN OCCUR.
 (4)  Open the thrust reversers (AMM 78-31-00/201).
 F.  Procedure
 S 215-006
 (1)  
Use a mirror to examine the position indicator on the precooler control valve.

 S 715-007

 (2)  
Is the precooler control valve in the fully open position?

 (a)  No, do the steps that follow for valve equipped with a manual wrenching hex, otherwise replace the precooler control valve (AMM 36-12-35/401). 1) Use a wrench on the manual wrenching hex to close and open
 the valve.
 2)  Does the valve move to the closed and open position smoothly? a) No, replace the precooler control valve
 (AMM 36-12-35/401).
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
 (b)  b) Yes, continue.Yes, continue.
 S 485-008
 (3)  Connect a supply pressure gage (Ps) and nitrogen source to the supply pressure inlet line at the tee from the 5th stage duct (View A, Fig. 501).
 S 485-013
 (4)  Install a control pressure gage (Pc) and a needle valve to the precooler control valve at the connection for the precooler control valve sensor (View B, Fig. 501).
 S 725-014
 (5)  With the needle valve in the closed position, slowly increase Ps to 14 psig.
 S 725-015
 (6)  Did the precooler control valve go to less than 30 degrees from the fully closed position? (a) No, do the steps that follow: 1) Slowly increase Ps to 70 psig. 2) Examine these areas for nitrogen leakage: a) Sense line to the precooler control valve b) Sense line between the precooler control valve and the precooler control valve sensor c) Precooler control valve sensor. 3) Repair all leakage found. a) If no leakage is found, replace the precooler control valve (AMM 36-12-35/401). 4) Decrease Ps to 0 psig. (b) Yes, continue.
 S 725-016
 (7)  Slowly increase Ps to 50-60 psig.
 S 225-017
 (8)  Is Pc between 6 and 12 psig, and the precooler control valve at less than 30 degrees from the fully closed position? (a) No, replace the precooler control valve (Ref 36-12-35/401). (b) Yes, continue.

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
SUPPLY LINE TO THE PRECOOLER CONTROL VALVE
SEE A
5TH-STAGE SUPPLY LINE
MS-6 (UNION) 
SUPPLY LINE 
TO THE BLEED 
AIR REGULATOR 
5TH-STAGE 
CHECK VALVE 
SUPPLY
PRESSURE 
GAUGE (Ps) 
TEST LINE  5TH-STAGE 
DUCT 
FWD 

NITROGEN PRESSURE
SUPPLY REGULATOR
PRESSURE
A
Precooler Control Valve Test EquipmentFigure 501 (Sheet 1)
　
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