(5)  
SSM 21-58-02

 B. Access
 (1)  Location Zone 121 Forward Cargo Compartment Forward Half, LH
 C. Prepare for the Removal
 S 862-024
 CAUTION: DO NOT OPERATE THE ELECTRICAL/ELECTRONIC EQUIPMENT WHEN YOU DO
_______ THIS PROCEDURE. IF YOU OPERATE THE ELECTRICAL EQUIPMENT WHEN THE EQUIPMENT COOLING SYSTEM IS OFF, YOU CAN CAUSE THE ELECTRICAL EQUIPMENT TO BECOME TOO HOT.
 (1)  
Remove the electrical power (Ref 24-22-00/201).

 S 012-003

 (2)  
Remove the left sidewall lining at station 520 of the forward cargo compartment (Ref 25-52-01/401).

 D. Remove the Switch
 S 032-004
 (1) Disconnect the electrical connector, DS1977, from the switch.
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747-400
MAINTENANCE MANUAL

STA 540
STA 520
AIR CLEANER (REF)
SEE A
FORWARD CARGO COMPARTMENT LEFT SIDEWALL
OVERHEAT SWITCH
SUPPLY  ELECTRICAL 
AIR DUCT  CONNECTOR 
A 

Equipment Cooling Overheat Switch - Maintenance Practices
Figure 201

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747-400 MAINTENANCE MANUAL
 S 032-015
 (2)  
Cut and remove the lockwire from the switch.

 S 022-005

 (3)  
Remove the switch.

 TASK 21-58-08-402-006
 4.  Equipment Cooling Overheat Switch Installation (Fig. 201)______________________________________________
 A. References
 (1)  
20-11-28/401, Lockwire

 (2)  
25-52-01/401, Containerized Cargo Compartment Ceiling and Sidewall Linings

 (3)  
IPC 21-58-08 Fig. 1

 (4)  
WDM 21-58-19

 (5)  
SSM 21-58-02

 B. Access
 (1)  Location Zone 121 Forward Cargo Compartment Forward Half, LH
 C. Install the Switch
 S 432-007
 (1)  
Put a new O-ring on the switch.

 S 422-016

 (2)  
Install the switch.

 (3)  
Install a lockwire on the switch (Ref 20-11-28/401).

 S 432-009

 (4)
Connect the electrical connector, DS1977, to the switch.

 S 432-008
 D. Put the Airplane to Its Usual Condition
 S 412-017
 (1)  Install the left sidewall lining in the forward cargo compartment (Ref 25-52-01/401).
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747-400 MAINTENANCE MANUAL
 DIFFERENTIAL PRESSURE SWITCH - REMOVAL/INSTALLATION
___________________________________________________
 1.  General_______
 A.  This procedure has instructions to remove and install the differential pressure switch for the equipment cooling system. The differential pressure switch is installed in the plenum at the top of the E1/E2 rack.
 TASK 21-58-09-004-001
 2.  Differential Pressure Switch Removal (Fig. 401)____________________________________
 A.  References
 (1)  
IPC 21-58-09 Fig. 1

 (2)  
WDM 21-58-19

 (3)  
SSM 21-58-02

 B.  Access
 (1)  Location Zone 117 Electrical and Electronics Compartment, LH
 C.  Prepare for the Removal
 S 864-002
 (1)  Make sure the EQUIP COOLING selector, on the overhead panel, P5, is in the NORM position.
 (a)  Put a DO-NOT-OPERATE tag on the selector.
　
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