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 ALL  ú ú 01 Page 216 ú Nov 15/97
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
 S 492-111
 (6)  Install the test equipment on the fuel line:
 (a)  
Disconnect the elbow fitting from the low-pressure fuel filter.

 (b)  
Remove the packing from the elbow fitting.
 1) Discard the packing.

 (c)  
Install the pressure gage on the elbow fitting.

 NOTE: The outer diameter of the elbow is 3/8 inch with a
____ 0.5625-18 thread (MIL-S-8879) (Male end fittings).
 S 912-092
 (7)  Supply external electrical power to the airplane (AMM 24-22-00/201).
 NOTE: The ac power is necessary to operate the fuel boost pump
____
 for the No. 1 fuel tank.

 S 862-098
 (8)  
Set the No. 1 AFT FUEL PUMP switch, on the P5 forward overhead panel, to the ON position.

 S 862-101

 (9)  
Remove the DO-NOT-CLOSE tag and close this circuit breaker:

 (a)  E3-3 Electrical Shelf, APU Control Unit
 S 862-102
 (10) Set the APU master switch to the ON position.
 NOTE:____Do not move the APU master switch to the START position. It is not necessary to start the APU.
 S 792-103
 (11) Monitor the fuel pressure to make sure there are no leaks:
 (a)  
Make sure the fuel pressure at the pressure gage is
 approximately 20 psig (138 kPa).

 (b)  
Set the No. 1 AFT FUEL PUMP switch, on the P5 forward overhead panel, to the OFF position.

 (c)  
Make sure the fuel pressure at the pressure gage does not decrease: 1) Monitor the fuel pressure on the pressure gage for 5

 minutes.
 2)  If there is not a decrease in pressure during the five minute time, then these check valves do not have leakage: a) APU Primary Check Valve
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 b) APU Bypass Check Valve
 c) APU Pressure Relief Valve

 3)  If there is a decrease in fuel pressure, do these steps to isolate the leakage in the APU fuel system:
 NOTE: A fuel leakage rate of 1 drop for each minute (2.5
____ cc for each hour) is permitted from the fuel control unit.
 a)  Set the No. 1 AFT FUEL PUMP switch on the P5 overhead panel to the ON position.
 b)  Make sure the pressure on the pressure gage is
 approximately 20 psig.
 c)  Set the APU master switch to the OFF position.
 d)  Set the No. 1 AFT FUEL PUMP switch, on the P5 overhead
 panel, to the OFF position.
 e)  Monitor the fuel pressure on the pressure gage for 5 minutes.
 f)  If there is a decrease in fuel pressure, correct all leaks or damage to the APU fuel system between the APU shutoff valve and the APU.
 g)  If there is no decrease in fuel pressure, then after you complete this procedure, do this procedure described below: "Leak Check of the APU Bypass Check Valve and Pressure Relief Valve".
 (d) Loosen the nut on the hose to bleed the fuel pressure.
 S 912-104
 (12)
 Remove the external electrical power from the airplane (AMM 24-22-00/201).

 S 862-118

 (13)
 Make sure the APU Master Switch is set to OFF.

 S 862-119

 (14)
 Open this circuit breaker and attach a DO-NOT-CLOSE tag:

 (a) E3-3 Electrical Shelf, APU Control Unit
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

 28-22-00
 ALL  ú ú 01 Page 218 ú Nov 15/97
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 S 092-107
 (15) Remove the test equipment:
 (a)  
Remove the pressure gage from the elbow.

 (b)  
　
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