YES 
NO
34 MEASURE THE RESISTANCE AT THE FUEL SOLENOID VALVE, 
CONNECTOR D1264, FROM PIN A TO 
PIN B (WDM 49-31-01). 
IS THE RESISTANCE 20-45 OHMS?
YES 
SEE SHEET 5 (BLOCK 35)
Circuit Breaker on the APU Control Unit 
Opens during the APU Operation 
Figure 109A (Sheet 4)
L37547
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FROM SHEET 4 (BLOCK 34) 
YES 
NO
35 MEASURE THE RESISTANCE AT THE IGNITION UNIT, CONNECTOR 
D1256, FROM PIN A TO CASE AND PIN B TO CASE (WDM 49-31-01). 
ARE THE RESISTANCES AMINIMUM OF 1000K OHMS?
YES 
NO
36 MEASURE THE RESISTANCE BETWEEN EACH SOCKET OF THE 
CONNECTOR FOR THE IGNITER CABLE. 
ARE THE RESISTANCES 0-0.1 OHMS (MAXIMUM)?
YES 
NO
37 MEASURE THE RESISTANCE BETWEEN EACH SOCKET AND THE 
CASE OF THE CONNECTOR FOR THE IGNITER CABLE. 
ARE THE RESISTANCES A MINIMUM OF 1000K OHMS?
YES 
YES
38 EXAMINE THE CIRCUIT FROM 
THE ELECTRONIC SPEED SWITCH 
(95% SWITCH; 110% SWITCH),
S634, CONNECTOR D1245, 
PINS, J, E, TO THE APU CONTROL 
UNIT, M280 CONNECTOR D50B,
PINS, 32, 35 (WDM 49-31-01). 
IS THERE A SHORT CIRCUIT?
NO 
YES
39 EXAMINE THE CIRCUIT FROMTHE SEQUENCING PRESSURE SWITCH 
FOR THE OIL TO THE APU CONTROL 
UNIT, M280 (WDM 49-31-01). 
IS THERE A SHORT CIRCUIT? 
NO
SEE SHEET 6 (BLOCK 40) 
Circuit Breaker on the APU Control Unit 
Opens during the APU Operation 
Figure 109A (Sheet 5)
L37590
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 ú  Jul 12/01 
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FROM SHEET 5 (BLOCK 39)
NO 
YES
40 EXAMINE THE CIRCUIT FROMTHE FUEL SOLENOID VALVE TO THE APU CONTROL UNIT, M280
(WDM 49-31-01, WDM 49-41-01). 
IS THERE A SHORT CIRCUIT?
NO 
YES41 EXAMINE THE CIRCUIT FROM THE IGNITION UNIT TO THE APU 
CONTROL UNIT, M280 
(WDM 49-31-01). 
IS THERE A SHORT CIRCUIT?
NO 
YES
42 EXAMINE THE CIRCUIT FROM THE IGNITER CABLE TO THE APU 
CONTROL UNIT, M280.
 IS THERE A SHORT CIRCUIT?
NO 
NO
43 EXAMINE THE APU HARNESS 
FOR WORN WIRES OR OTHER 
DAMAGE.
IS THE APU HARNESS OK?
Circuit Breaker on the APU Control Unit Opens during the APU Operation Figure 109A (Sheet 6) 
L37597
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 ú  02  Page 136 
 ú  Jul 12/01 
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FROM SHEET 4 (BLOCK 2) YES
NO
44 MOVE THE APU MASTER SWITCH 
TO THE "OFF" POSITION.
MEASURE THE RESISTANCE AT THE STARTER MOTOR, M161, POSITIVE TO NEGATIVE TERMINALS (WDM 49-31-01). 
IS THE RESISTANCE 0.1 OHMS (MAXIMUM)?
YES 
YES
45 EXAMINE THE CIRCUIT FROM THE INLET DOOR ACTUATOR, M299,
CONNECTOR D922, PIN 1, TO THE 
APU CONTROL UNIT, M280, 
CONNECTOR D50B, PIN 49 
(WDM 49-31-01).
 IS THERE A SHORT CIRCUIT?
NO 
YES
 
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