YES NO YES

2 DO THE APU USUAL SHUTDOWN
21 DO A CHECK OF THE FUEL
(AMM 49-11-00/201). SENSING FLOW CONTROL VALVE
DO THE FLOW CHECK OF THE (AMM 49-31-92/501). FUEL SUPPLY SYSTEM FOR THE APU DOES THE FLOW CONTROL (AMM 49-31-00/501). VALVE OPERATE CORRECTLY?

SEE SHEET 2 (BLOCK 3)
APU Engine Speed Decreases Too Much When a Bleed Load Is Applied
Figure 121 (Sheet 1)

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / GTCP85-129 SERIES /737-300/400/500/ ENGINES /MAINTENANCE MANUAL ////////////////////////
FROM SHEET 1 (BLOCK 2)

YES
YES

3 DO THE APU DRY MOTORING
(AMM 49-11-00/201).
DID A CONTINUOUS FLOW OF FUEL COME FROM THE FUEL LINE FOR THE FUEL ATOMIZER?

FOR THE LOW-PRESSURE FUEL AND FUEL FILTER ELEMENT THE HIGH-PRESSURE FUEL. (AMM 49-31-22/401) AND CLEAN ARE THE FUEL FILTERS THE HIGH-PRESSURE FUEL FILTERCLOGGED?(AMM 49-31-81/301), AS NECESSARY.

NO
IF THE PROBLEM CONTINUES, GO TO BLOCK 5.
NO

5 REPLACE THE FUEL CONTROL
UNIT (AMM 49-31-11/401).
 START AND OPERATE THE APU
(AMM 49-11-00/201).
DOES THE PROBLEM CONTINUE?

YES YES

6 DO THE LEAK CHECK FOR THE
CONTROL AIR (AMM 49-11-00/
201).

IS THERE LEAKAGE IN THE CONTROL AIR LINES?
NO
YES

22 DO A CHECK OF THE TEE FITTING ON THE CONTROL AIR LINE.
IS THE TEE FITTING CLOGGED?
NO

APU Engine Speed Decreases Too Much When a Bleed Load Is Applied
Figure 121 (Sheet 2)

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A13028
A 737-300/400/500MAINTENANCE MANUAL
EGT IS TOO HIGH OR  PREREQUISITES 
OUT OF CONTROL DUR- NONE 
ING THE APPLICATION 
OF THE BLEED LOAD 

POSSIBLE CAUSES:
1.
REGULATOR FOR THE DIFFERENTIAL AIR PRESSURE PROBLEM (AMM 49-52-21/401)

2.
APU CONTROL THERMOSTAT PROBLEM (AMM 49-52-32/401)

3.
CLOGGED TEE FITTING FOR THE CONTROL AIR LINE

4.
3-WAY SOLENOID VALVE PROBLEM (AMM 49-52-61/401)

5.
BLEED AIR VALVE, V56, PROBLEM (AMM 49-52-11/401).

FAULT ISOLATION:
//////////////////////// / GTCP85-129 SERIES / / ENGINES / ////////////////////////

SEE SHEET 2 (BLOCK 2)
EGT Is Too High or Out of Control during the Application of the Bleed Load
Figure 122 (Sheet 1)

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A53610
////////////////////////A / GTCP85-129 SERIES /737-300/400/500/ ENGINES /MAINTENANCE MANUAL ////////////////////////
FROM SHEET 1 (BLOCK 1)
YES

YES
2
MAKE SURE THE TEE FITTING
52 CLEAN THE TEE FITTING FOR FOR THE CONTROL AIR LINE IS THE CONTROL AIR LINE NOT CLOGGED. (AMM 49-52-91/701) OR REPLACE
THE TEE FITTING.
NOTE:THE ORIFICE OF THE TEE FITTING MUST BE 0.080 TO 0.084 INCH
(2.03 TO 2.13 mm).
 IS THE TEE FITTING CLOGGED?

NO NO

3 DO A CHECK OF THE INSTAL-
53 REMOVE AND INSTALL THE
LATION OF THE 3-WAY SOLENOID 3-WAY SOLENOID VALVE OR
VALVE. REPLACE THE VALVE

IS THE 3-WAY SOLENOID (AMM 49-52-61/401). VALVE INSTALLED CORRECTLY?
YES NO

21 DO THE TEST OF THE APU
54 ADJUST THE APU CONTROL CONTROL THERMOSTAT THERMOSTAT (AMM 49-52-32/501). (AMM 49-52-32/501). IF THE APU CONTROL THERMO-
IS THE SET POINT FOR THE STAT WILL NOT CORRECTLY APU CONTROL THERMOSTAT BETWEENADJUST, REPLACE THE THERMOSTAT 620-649`C? (AMM 49-52-32/401).
　
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