TERMINAL WIRING
THERMAL SWITCH
Thermal Switches Check
Figure 601
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747-400 MAINTENANCE MANUAL
C. Procedure
S 866-002
(1) Open these circuit breakers:
(a) P6 Main Power Distribution Panel 1) 6C5 ALTN PWR LOOP A APU FIRE/BLD DUCT OVHT 2) 6H14 APU FIRE/BLD DUCT OVHT LOOP A 3) 6H15 APU FIRE/BLD DUCT OVHT LOOP B
S 016-011
WARNING: MAKE SURE THAT PERSONS AND EQUIPMENT ARE CLEAR OF THE LE AND TE
_______ FLAPS AND FLAP DRIVE MECHANISMS BEFORE YOU MOVE THE FLAP CONTROL LEVER. WITH THE HYDRAULIC POWER REMOVED, THE FLAPS MOVE AUTOMATICALLY BY ELECTRICAL POWER WHEN YOU MOVE THE FLAP CONTROL LEVER.
(2) Extend the wing leading edge flap for access to the thermal switches (AMM 27-81-00/201).
S 496-004
WARNING:_______REFER TO 27-81-00/201 FOR LOCK INSTALLATION PROCEDURE. INSTALL LOCKS TO PREVENT INJURY FROM INADVERTENT OPERATION OF FLAPS.
(3)
Install safety locks on all extended leading edge flaps when persons work in the area of the wing leading edge area.
S 016-005
(4)
Remove the access panels as required to get to the strut thermal switches. Refer to AMM 06-09-08 for access door identification.
(5)
Make a check of the thermal switches for damage or corrosion.
(6)
Install the access panels that were removed.
S 216-006
S 416-007
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S 096-008
WARNING:_______REFER TO 27-81-00/201 FOR LOCK REMOVAL PROCEDURE. THE FLAPS WILL RETRACT IN 7 SECONDS AND MAY INJURE PERSONS.
(7) Remove the leading edge flap safety locks (AMM 27-81-00/201).
S 416-010
WARNING: MAKE SURE THAT PERSONS AND EQUIPMENT ARE CLEAR OF THE LE AND TE
_______ FLAPS AND FLAP DRIVE MECHANISMS BEFORE YOU MOVE THE FLAP CONTROL LEVER. WITH HYDRAULIC POWER REMOVED, THE FLAPS WILL MOVE AUTOMATICALLY BY ELECTRICAL POWER WHEN YOU MOVE THE FLAP CONTROL LEVER.
(8)
Retract the wing leading edge flaps (AMM 27-81-00/201).
S 866-009
(9)
Close these circuit breakers:
(a) P6 Main Power Distribution Panel
1) 6C5 ALTN PWR LOOP A APU FIRE/BLD DUCT OVHT
2) 6H14 APU FIRE/BLD DUCT OVHT LOOP A
3) 6H15 APU FIRE/BLD DUCT OVHT LOOP B
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747-400 MAINTENANCE MANUAL
APU DUCT OVERHEAT DETECTION SYSTEM - DESCRIPTION AND OPERATION
______________________________________________________________
General
_______
A. The APU duct overheat detection system monitors the air temperature around the APU bleed air duct. The system includes thermal switches, an indicator light and a reset switch.
B. Twenty thermal switches are installed along the APU bleed air duct. Fifteen are installed in the aft cargo compartment and five are installed in the area aft of the bulk cargo compartment. All switches are set to close at 250 degrees F.
C. On all airplanes, seven more thermal switches are installed along the APU bleed air duct between the APU check valve and the APU isolation valve. The thermal switches monitor air temperature for an overheat condition caused by a APU duct leak or break.
D. Under the normal conditions, the thermal switches are in the open position. An overheat condition caused by a leakage or breaks in the duct causes the thermal switch to close, the indicator light to come on, and the EICAS message to show.
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