2.
EXTERNAL DAMAGE TO THE APU

3.
ADJUSTMENT OF THE APU AIR INLET (AMM 49-15-00/501)

4.
APU INTERNAL DAMAGE (AMM 49-11-00/401)

5.
ELECTRONIC SPEED SWITCH, S634, PROBLEM (AMM 49-61-22/401)

6.
P5-10 AIR CONDITIONING MODULE PROBLEM (AMM 21-51-01/401).

FAULT ISOLATION:
YES

1 DO A CHECK OF THE CIRCUIT
51 DO THIS PROCEDURE:
BREAKER FOR THE APU CONTROL CIRCUIT BREAKER ON THE APU
UNIT.CONTROL UNIT OPENS DURING THE
IS THE CIRCUIT BREAKER APU OPERATION (FIG. 109). OPEN?

NO NO

1A DO A CHECK OF THE
CONNECTOR PINS FOR THE
ELECTRONIC SPEED SWITCH.

ARE THE CONNECTOR PINS GOOD?

YES NO
2 MEASURE THE RESISTANCE AT
THE ELECTRONIC SPEED SWITCH,
S634, CONNECTOR D1245, FROM
PINS, F TO M, K TO L

(WDM 49-31-01).
ARE THE RESISTANCES LESS THAN 100 OHMS?

COMPONENTS OF THE APU FUEL COMPONENTS AS NECESSARY. SYSTEM.
IS THERE DAMAGE TO OR LEAKAGE FROM THE COMPONENTS OF THE APU FUEL SYSTEM?

NO SEE SHEET 2
(BLOCK 4)

Automatic Shutdown - No Apparent Cause
Figure 140A (Sheet 1)

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L37977
FROM SHEET 1 (BLOCK 3) NO

4

DO A VISUAL CHECK OF THE EXTERNAL PARTS OF THE APU. IS THERE DAMAGE TO THE APU?

NO
5

DO THE TEST FOR THE APU AIR INLET (AMM 49-15-00/501). DOES THE APU AIR INLET OPERATE CORRECTLY?

YES
6 DO A CHECK OF THE OIL FILTER ELEMENT (AMM 49-91-12/401).
DOES THE OIL FILTER ELEMENT HAVE METAL PARTICLES?
NO

YES

YES

NO

YES

NO

NO

21 START AND OPERATE THE APU

(AMM 49-11-00/201).
DOES THE APU SHUTDOWN WITH
NO APPARENT CAUSE?
YES

59 REPLACE THE APU (AMM 49-11-00/401).
58 DO THE APU USUAL SHUTDOWN (AMM 49-11-00/201).
CONTINUE THE APU OPERATION.

Automatic Shutdown - No Apparent Cause
Figure 140A (Sheet 2)

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L37980
////////////////////////A / GTCP85-129 SERIES /737-300/400/500/ ENGINES /MAINTENANCE MANUAL ////////////////////////
APU USUAL SHUTDOWN - PREREQUISITES 
"OVERSPEED" LIGHT  NONE 
IS ON 

POSSIBLE CAUSES:
1.
APU CONTROL UNIT, M280, PROBLEM (AMM 49-61-11/401)

2.
ELECTRONIC SPEED SWITCH, S634, PROBLEM (AMM 49-61-22/401).

FAULT ISOLATION:
NO NO

1 MAKE SURE THE APU MASTER
21 MOVE THE APU MASTER SWITCH
SWITCH IS IN THE "OFF" TO THE "ON" POSITION.
POSITION. DID THE "OVERSPEED" LIGHT
DOES THE APU CONTROL UNIT GO OFF? HAVE THE "TEST PASS" AND "TEST
YESFAIL" LIGHTS?
YES NO
2 PUSH THE "OVERSPEED RESET/

TEST" BUTTON ON THE APU
CONTROL UNIT.
DID THE "TEST PASS" LIGHT (GREEN) COME ON?
YES NO
3 EXAMINE THE CIRCUIT FROM THE ELECTRONIC SPEED SWITCH,
S634, CONNECTOR D1245, PIN E,
TO THE APU CONTROL UNIT, M280,
CONNECTOR D50B, PIN 35
(WDM 49-31-01).
IS THE CIRCUIT OK?
YES

51 MOVE THE APU MASTER SWITCH TO THE "OFF" POSITION. REPLACE THE APU CONTROL UNIT, M280 (AMM 49-61-11/401).
APU Usual Shutdown - OVERSPEED Light Is On
Figure 141

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