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 21-44-04
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A
747-400 MAINTENANCE MANUAL
 AFT CARGO UNDERFLOOR HEAT CONTROL SWITCH - REMOVAL/INSTALLATION
_______________________________________________________________
 1.  General_______
 A.  There are two tasks in this procedure. There is one task for the removal and one task for the installation of the aft cargo underfloor heat control switch. The procedure has these parts:
 (1)  
The removal of power to the aft cargo underfloor heat control switch.

 (2)  
The removal of a floor panel in the bulk cargo compartment to get access to the aft cargo underfloor heat control switch.

 (3)  
The removal of the aft cargo underfloor heat control switch.

 (4)  
The installation of the aft cargo underfloor heat control switch.

 (5)  
A functional test of the aft cargo underfloor heat control switch.

 B.  The aft cargo underfloor heat control switch is a thermal switch which controls the flow of hot air to the area below the compartment floor when the aft cargo air conditioning system is on.
 C.  The aft cargo underfloor heat control switch is installed on a floor beam immediately inside of the bulk cargo door.
 TASK 21-44-07-004-001
 2.  Switch Removal (Fig. 401)______________
 A.  References
 (1)  
IPC 21-61-51 Fig. 10

 (2)  
WDM 21-44-11

 (3)  
SSM 21-44-01

 B.  Access
 (1)  Location Zone
 146 Bulk Cargo Compartment, RH

 C.  Procedure
 S 864-002
 (1)  Open the following circuit breaker for the aft cargo underfloor heat control switch and attach a DO-NOT-CLOSE tag.
 (a)  On the P7 Overhead Circuit Breaker Panel 1) 7H9 CARGO HEAT AFT
 S 014-003
 (2)
Remove the floor panel in the bulk cargo compartment at station 2020, 2 1/2 feet (762 mm) right of the airplane centerline.

 (3)  
Remove the electrical connector DS2071 from the switch.

 (4)  
Remove the nut from the switch and remove the switch.

 S 034-004
 S 024-005
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747-400
MAINTENANCE MANUAL

Aft Cargo Underfloor Heat Control Switch Installation
Figure 401

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 21-44-07
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747-400
MAINTENANCE MANUAL

 TASK 21-44-07-404-006
 3. Switch Installation
___________________
 A. Standard Tools and Equipment
 (1)  
Cooling source - ice pack or equivalent which can cool the surface to less than 32°F (0°C).

 (2)  
Heating medium - Hot water bottle or other controlled source of heat.

 B. References
 (1)  
20-11-28/401, Lockwire

 (2)  
24-22-00/201, Manual Control

 (3)  
36-00-00/201, Pneumatic System

 (4)  
IPC 21-61-51 Fig. 10

 (5)  
WDM 21-44-11

 (6)  
SSM 21-44-02

 C. Access
 (1)  Location Zone
 145 Bulk Cargo Compartment, LH

 D. Procedure
 S 424-007
 (1)  
Put the switch on the bracket with the probe end pointed inboard and install the nut.

 S 434-008
　
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