(4)  
Disconnect the electrical connector, DV351 from the applicable engine start valve (Refer to 80-11-02/401 to get access to the start valve).

 S 866-145

 (5)  
Remove the DO-NOT-CLOSE tag and close this circuit breaker:

 (a)  
Main Power Distribution Panel, P6
 1) 6J18 ENG START AIR CONT

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747-400 MAINTENANCE MANUAL
 (6)  S 866-035Put the left isolation valve switch to close and the right isolation valve switch to open.
 (7)  S 866-146Put the APU VALVE switch to the ON position.
 (8)  S 866-037Pull out the applicable engine start switch on the P5 overhead panel.
 S 866-148

 WARNING: USE A RATCHET WRENCH TO TURN THE PRV MANUAL OVERRIDE DRIVE.
_______ THE PRV CAN OPEN QUICKLY WHEN YOU TURN THE MANUAL OVERRIDE DRIVE. THIS CAN PULL THE WRENCH OUT OF YOUR HANDS AND CAN CAUSE INJURIES TO PERSONS OR DAMAGE TO EQUIPMENT
 (9)  
Carefully turn the PRV manual override drive on the applicable engine to the OPEN position.

 (a)  
Make sure that the PRV stays in the open position.

 S 866-038
 (10)
 Put the APU VALVE switch to the OFF position when the MANIFOLD DUCT PRESSURE is stable.

 S 216-039

 (11)
 Monitor the MANIFOLD DUCT PRESSURE on the auxiliary EICAS display and let the duct pressure fall to 30 psi by natural decay.

 (a)  
When the duct pressure reaches 30 psi, begin the stop watch or the pilot's clock to check the time necessary for the duct pressure to drop to 15 psi.

 S 796-040
 (12) If the time noted is 14 seconds or more, the system is acceptable. Otherwise, examine and repair the leakages from couplings, ducts, precooler, and equipment.
 NOTE: A small quantity of leakage is permitted at the joints.
____ There must not be a high quantity of leakage at the joints. A high quantity of leakage can be felt by the hand from 12 inches away.
 S 866-033
 (13)
 Open this circuit breaker and attach a DO-NOT-CLOSE tag:

 (a)  
P6 Main Power Distribution Panel 1) 6J18 ENG START AIR CONT

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747-400 MAINTENANCE MANUAL
 S 866-041
 (14)
 Push the applicable engine start switch in to the off position.

 S 436-042

 (15)
 Connect the electrical connector, DV351 to the applicable engine start valve.

 S 866-044

 (16)
 Release the pressure from the pneumatic system if it is no longer necessary for other operations (Ref 36-00-00/201).

 H. Put the Airplane Back to Its Usual Condition
 S 866-011
 (1)  
Put the left isolation valve to open.

 S 866-055

 (2)  
Make sure the right isolation valve is open.

 S 866-053

 (3)  
Shut down the APU (Ref 49-11-00/201).

 S 866-029

 (4)  
Open this circuit breaker and attach a DO-NOT-CLOSE tag:

 (a)  
P6 Main Power Distribution Panel
 1) 6K18 APU ALTN CONT

 S 866-030
 (5)  
Open these circuit breakers and attach DO-NOT-CLOSE tags:

 (a)  
P83 Panel, E8 Aft Equipment Center
 1) APU PRIMARY CONT
 2) APU START

 (6)  
Remove the APU controller, M7847 (Ref 49-61-07/401).

 S 026-047
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