CONNECTOR D920, PINS, 1, 2 AND
4, TO THE APU CONTROL UNIT,
M280, CONNECTOR D50B, PINS, 8,
13 AND 27 (WDM 49-31-01).
IS THERE A SHORT CIRCUIT?

NO

87 REPAIR THE PROBLEMS THAT YOU FIND.
 IF THE PROBLEM CONTINUES, REPLACE THE INLET DOOR ACTUATOR, M299 (AMM 49-15-31/401).

88 REPAIR THE PROBLEMS THAT YOU FIND.
 IF THE PROBLEM CONTINUES, REPLACE THE APU FUEL VALVE, V43 (AMM 28-22-31/401).
YES

47 EXAMINE THE CIRCUIT FROM
THE STARTER MOTOR, M161, TO

THE APU CONTROL UNIT, M280 (WDM 49-31-01).
 IS THERE A SHORT CIRCUIT?
NO
NO

YES
NO
49 MANUALLY TURN THE APU (AMM 49-21-00/201).
 ARE THERE UNUSUAL NOISES WHEN THE APU TURNS OR DOES THE APU NOT TURN AS USUAL?
YES

Circuit Breaker on the APU Control Unit Opens during the APU Operation Figure 109A (Sheet 7)
L37600
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. APU WITH THE ELECTRONIC SPEED SWITCH ú
 49-00-00
 PART NUMBER 3876259  ú
 ú  02  Page 137
 ú  Jul 12/01 

BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / GTCP85-129 SERIES /737-300/400/500/ ENGINES /MAINTENANCE MANUAL ////////////////////////
PREREQUISITES 
MAKE SURE THIS SYSTEM WILL OPERATE: APU (AMM 49-11-00/201)
NOT TURN STARTER MOTOR DOES  MAKE SURE THE AIRPLANE IS IN THIS CONFIGURATION: ELECTRICAL POWER IS ON (AMM 24-22-00/201) 

POSSIBLE CAUSES:
1.STARTER MOTOR, M161, PROBLEM (AMM 49-41-11/401)
2.
START RELAY, R5, PROBLEM (WDM 49-31-01)

3.
ELECTRONIC SPEED SWITCH, S634, PROBLEM (AMM 49-61-22/401)

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

5.
APU MASTER SWITCH, S248, PROBLEM (WDM 49-31-01).

FAULT ISOLATION:
NO

1 MAKE SURE THE POSITIVE
LEAD AND NEGATIVE LEAD FOR THE
STARTER MOTOR ARE INSTALLED ON
THE CORRECT STARTER MOTOR TER-

MINALS.
ARE THE LEADS FOR THE STARTER MOTOR CORRECTLY INSTALLED?

YES NO

2 MOVE THE APU MASTER SWITCH
52 MOVE THE APU MASTER SWITCH TO THE "ON" POSITION. TO THE "OFF" POSITION. DID THE AIR INLET DOOR DO THIS PROCEDURE: THE FULLY OPEN?AIR INLET DOOR DOES NOT FULLY OPEN (FIG. 108).

YES NO
3 MOVE THE APU MASTER SWITCH
TO THE "OFF" POSITION.
 DISCONNECT THE NEGATIVE LEAD FROM THE STARTER MOTOR.

EXAMINE THE NEGATIVE LEAD TO GROUND (WDM 49-31-01).
 IS THE CIRCUIT OK?

YES SEE SHEET 2
(BLOCK 4)

Starter Motor Does Not Turn
Figure 110 (Sheet 1)

EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. APU WITH THE ELECTRONIC SPEED SWITCH ú
 49-00-00
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 ú  02  Page 138
 ú  Jul 12/01 

BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A12470
////////////////////////A / GTCP85-129 SERIES /737-300/400/500/ ENGINES /MAINTENANCE MANUAL ////////////////////////
FROM SHEET 1 (BLOCK 3)
YES NO NO

21 _______
WARNING
DO NOT OPERATE THE APU WITH YES
THE LOWER SHROUD REMOVED IF PERSONS ARE IN OR DIRECTLY BELOW THE APU COMPARTMENT. SEE SHEET 4
YOU MUST BE A MINIMUM OF
(BLOCK 5) 3 FEET AWAY FROM THE OUTER EDGE OF THE APU COMPARTMENT OPENING TO OPERATE THE APU WITH THE LOWER SHROUD REMOVED. AN APU TURBINE WHEEL SEPARA-TION DURING OPERATION CAN CAUSE INJURY TO PERSONS.
CONNECT THE NEGATIVE LEAD
TO THE STARTER MOTOR. REPLACE THE STARTER MOTOR,
M161 (AMM 49-41-11/401). DOES THE PROBLEM CONTINUE? YES YES
22 EXAMINE THE CIRCUIT FROM TERMINAL X1 TO TERMINAL X2 OF THE START RELAY, R5 (WDM 49-31-01).

IS THERE AN OPEN CIRCUIT?

NO NO

23 DO A CHECK FOR 28V DC AT THE START RELAY, R5, TERMINAL A1 (WDM 49-31-01).

 IS THERE 28V DC AT TERMINAL A1?
YES NO
24 EXAMINE THE CIRCUIT FROM THE START RELAY, R5, TERMINAL X1, TO THE APU CONTROL UNIT, M280, CONNECTOR D50B, PIN 30 (WDM 49-31-01).

IS THE CIRCUIT OK?

YESNO
25 EXAMINE THE CIRCUIT FROMTHE START RELAY, R5, TERMINAL A2, TO THE STARTER MOTOR, M161, POSITIVE TERMINAL (WDM 49-31-01).
　
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