BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
FROM SHEET 1 (BLOCK 3)

YES
YES

4 CONNECT THE LOW OIL PRES-SURE SWITCH, CONNECTOR D1254.
 MOVE THE APU MASTER SWITCH
TO THE "ON" POSITION.

DO A CHECK FOR 28V DC AT THE P5-4 MODULE FOR THE APUAND AC SYSTEM GENERATOR, CONNECTOR D634, PIN 8(WDM 49-41-01).
 IS THERE 28V DC AT PIN 8?
NO

55 MOVE THE APU MASTER SWITCH TO THE "OFF" POSITION.
REPLACE THE P5-4 MODULE FOR THE APU AND AC SYSTEM GENERATOR (WDM 49-41-01).

NO
22 MOVE THE APU MASTER SWITCH TO THE "OFF" POSITION.
EXAMINE THE CIRCUIT FROM THE P5-4 MODULE FOR THE APU AND AC SYSTEM GENERATOR, CONNECTOR D634, PIN 8, TO THE APU CONTROL UNIT, M280, CONNECTOR D50B, PIN 25 (WDM 49-41-01).
EXAMINE THE CIRCUIT FROM THE LOW OIL PRESSURE SWITCH, CONNECTOR D1254, PIN 2, TO THE APU CONTROL UNIT, M280, CONNECTOR D50B, PIN 26 (WDM 49-41-01).
ARE THE CIRCUITS OK?
YES

LOW OIL PRESSURE Light Does Not Come On When the APU Master Switch
Moves to the ON Position from the OFF Position
Figure 106 (Sheet 2)

A13810
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////////////////////////
A / GTCP85-129 SERIES /
THE APU FUEL VALVE DOES NOT FULLY OPEN OR DOES NOT FULLY CLOSE

POSSIBLE CAUSES:
737-300/400/500/ ENGINES /MAINTENANCE MANUAL ////////////////////////
PREREQUISITES
MAKE SURE THESE CIRCUIT BREAKERS ARE CLOSED: P6-5 - C33 APU CONTROL UNIT
MAKE SURE THE AIRPLANE IS IN THIS CONFIGURATION: ELECTRICAL POWER IS ON (AMM 24-22-00/201)
1.
APU FUEL VALVE, V43, PROBLEM (AMM 28-22-31/401)

2.
APU CONTROL UNIT, M280, PROBLEM (AMM 49-61-11/401)

3.
APU MASTER SWITCH, S248, PROBLEM.

FAULT ISOLATION:
NO

1 WITH THE APU MASTER SWITCH
IN THE "OFF" POSITION, MAKE
SURE THE APU FUEL VALVE IS
FULLY CLOSED.

NOTE: THE APU FUEL VALVE IS ON THE REAR SPAR OF THE LEFT WING IN THE WHEEL WELL. THE MANUAL OVER-RIDE HANDLE ON THE APU FUEL VALVE GIVES AN INDICATION OF THE VALVE POSITION.
IS THE APU FUEL VALVE FULLY CLOSED?

YES SEE SHEET 2 (BLOCK 2)
YES

21 DO A CHECK FOR 28V DC AT
THE APU FUEL VALVE, V43,

CONNECTOR D920, PIN 2 (WDM 49-31-01). IS THERE 28V DC AT PIN 2?

NO
NO

22 REMOVE THE APU CONTROL
UNIT (AMM 49-61-11/401).

CLOSE THE "APU CONT" CIRCUIT BREAKER ON THE P6-5LOAD CONTROL CENTER.
DO A CHECK FOR 28V DC AT THE APU CONTROL UNIT, M280,CONNECTOR D50B, PIN 5 (WDM 49-31-01).
IS THERE 28V DC AT PIN 5?
YES

52 INSTALL THE APU CONTROL UNIT, M280 (AMM 49-61-11/401).
REPAIR THE CIRCUIT FROM THE APU CONTROL UNIT, M280,CONNECTOR D50B, PIN 5, TO THE"APU CONT" CIRCUIT BREAKER ON THE P6-5 LOAD CONTROL CENTER (WDM 49-31-01).
YES

23 DO A CONTINUITY CHECK
AT THE APU CONTROL UNIT,
M280, CONNECTOR D50B, PINS 5
AND 3, PINS 14 AND 13
(WDM 49-31-01).

IS THERE AN OPEN CIRCUIT?
NO
YES

24 INSTALL THE APU CONTROL
UNIT, M280 (AMM 49-61-11/401).

DO A CONTINUITY CHECK AT THE APU MASTER SWITCH, S248, CONNECTOR D4218P, PINS 2 AND 3 (WDM 49-31-01).
IS THERE AN OPEN CIRCUIT?

NO
SEE SHEET 2 (BLOCK 25)
The APU Fuel Valve Does Not Fully Open or Does Not Fully Close
Figure 107 (Sheet 1)

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
FROM SHEET 1 FROM SHEET 1 (BLOCK 1) (BLOCK 24)
YES NO
NO
YES
YES

2 MOVE THE APU MASTER SWITCH
TO THE "ON" POSITION.
 MAKE SURE THE APU FUEL
VALVE IS FULLY OPEN.
DID THE APU FUEL VALVE
FULLY OPEN?
　
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