NO
NO

YES YES

26 DO A CHECK FOR 28V DC AT
THE APU FUEL VALVE, V43,
CONNECTOR D920, PIN 1
(WDM 49-31-01).

IS THERE 28V DC AT PIN 1?
NO NO
27 REMOVE THE APU CONTROL UNIT, M280 (AMM 49-61-11/401).
 CLOSE THE "APU CONT" CIRCUIT BREAKER ON THE P6-5 LOAD CONTROL CENTER.
DO A CHECK FOR 28V DC ATTHE APU CONTROL UNIT, M280,CONNECTOR D50B, PIN 5 (WDM 49-31-01).
IS THERE 28V DC AT PIN 5?
YES
56 REPAIR THE CIRCUITS FROM THE APU CONTROL UNIT, M280, CONNECTOR D50B, PINS 3,14, TO THE APU MASTER SWITCH, S248, CONNECTOR D4218J, PINS 2,3 (WDM 49-31-01).

60 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).
SEE SHEET 3 (BLOCK 28)
The APU Fuel Valve Does Not Fully Open or Does Not Fully Close
Figure 107 (Sheet 2)

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A13825
////////////////////////
A / GTCP85-129 SERIES /
737-300/400/500/ ENGINES /MAINTENANCE MANUAL ////////////////////////
FROM SHEET 2 (BLOCK 27)

YESYES

28 DO A CONTINUITY CHECK
AT THE APU CONTROL UNIT,
M280, CONNECTOR D50B, PINS 5
AND 3, PINS 43 AND 8
(WDM 49-31-01).

IS THERE AN OPEN CIRCUIT?

NO
YES29 INSTALL THE APU CONTROLUNIT, M280 (AMM 49-61-11/401).
MAKE SURE THE APU MASTER SWITCH IS IN THE "ON" POSI-TION.
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?

THE APU FUEL VALVE, V43, CONNECTOR D920, PIN 1 (WDM 49-31-01).
 IS THE CIRCUIT OK?

REPAIR THE CIRCUITS FROM THE APU CONTROL UNIT, M280, CONNECTOR D50B, PINS 3,43, TO THE APU MASTER SWITCH, S248, CONNECTOR D4218J, PINS 2,4 (WDM 49-31-01).
The APU Fuel Valve Does Not Fully Open or Does Not Fully Close
Figure 107 (Sheet 3)

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A13826
THE AIR INLET DOOR PREREQUISITES DOES NOT FULLY OPEN
MAKE SURE THESE CIRCUIT BREAKERS ARE CLOSED: OR DOES NOT FULLY P6-5 - C33 CLOSE APU CONTROL UNIT

MAKE SURE THE AIRPLANE IS IN THIS CONFIGURATION: ELECTRICAL POWER IS ON (AMM 24-22-00/201) POSSIBLE CAUSES:
1.
DAMAGED OR BLOCKED AIR INLET DOOR (AMM 49-15-22/401)

2.
INLET DOOR ACTUATOR PROBLEM (AMM 49-15-31/401)

3.
APU FUEL VALVE, V43, PROBLEM (AMM 28-22-31/401)

4.
APU CONTROL UNIT, M280, PROBLEM (AMM 49-61-11/401).

FAULT ISOLATION:
NO YES

1 WITH THE APU MASTER SWITCH
21 EXAMINE THE AIR INLET
51 REPAIR OR REPLACE THE
IN THE "OFF" POSITION, MAKE DOOR, INLET DOOR ACTUATOR AND PARTS THAT ARE NECESSARY
SURE THE AIR INLET DOOR IS THE RELATED PARTS. (AMM 49-15-22/401;
FULLY CLOSED. ARE THE PARTS DAMAGED OR AMM 49-15-31/401).

IS THE AIR INLET DOOR CAUGHT?FULLY CLOSED?

NO
YES
NO

22 MAKE SURE THE APU FUEL
52 DO THIS PROCEDURE: THE SEE SHEET 2 VALVE IS FULLY CLOSED. APU FUEL VALVE DOES NOT FULLY (BLOCK 2)
CLOSE (FIG. 107).
____ THE APU FUEL VALVE IS
NOTE: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
YES
23 DO A CHECK FOR 28V DC AT
THE INLET DOOR ACTUATOR, M299,
CONNECTOR D922, PIN 1
(WDM 49-31-01).

IS THERE 28V DC AT PIN 1?

NO
SEE SHEET 2(BLOCK 24)
The Air Inlet Door Does Not Fully Open or Does Not Fully Close
Figure 108 (Sheet 1)

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