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)

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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)

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 ú  02  Page 135
 ú  Jul 12/01 

BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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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)
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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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