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 ALL  ú ú 13 Page 406 ú Jun 10/93
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400 MAINTENANCE MANUAL
 EQUIPMENT COOLING SYSTEM - DESCRIPTION AND OPERATION
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General (Fig. 1)
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 A.  Electrical/electronic (E/E) equipment generates heat which must be dissipated by forced air circulation cooling.
 B.  The equipment cooling system removes the heat through the use of cooling airflow. Heated airflow removed from the equipment is ducted into the forward cargo compartment or overboard.
 C.  The equipment cooling system consists of a forward and aft system.
 (1)  
The forward system provides both blow through and draw through cooling.

 (a)  The forward equipment cooling system is located in body section 41 (Flight deck and lower lobe area) and body section 43 (forward cargo compartment area).

 (2)  
The aft system provides draw through cooling and is automatic in operation.

 (a)  The aft equipment cooling system is located in the area behind
 the bulk cargo compartment.Inboard Valves
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 A.  The equipment cooling system uses three 9-inch diameter electric shutoff valves: an inboard supply valve, inboard exhaust valve, and bypass valve. The valves control air flow path through the equipment cooling system.
 B.  The equipment cooling inboard valves are motor operated valves with manual override and exterior visual position indication. All three valves are powered by 115 volt ac from the 115 vac bus 2 and 28 volt dc from the 28 vdc bus 1.
Ground Exhaust Valve
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 A.  During ground operations, with forward cargo compartment temperature greater than approximately 45°F (7°C) equipment cooling airflow is exhausted overboard through the ground exhaust valve. The ground exhaust valve is a motor actuated flapper valve. The valve consists of a flapper operated by an electrical actuator. A manual override socket allows manual flapper positioning from outside the airplane.
 B.  The ground exhaust valve is powered by 115 volt ac from the 115 vac bus 1
 and 28 volt dc from the 28 vdc bus 1.Smoke/Override Valve
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 A.  In flight, with the system in override mode, cooling air is exhausted overboard through the smoke/override valve. The smoke/override valve is a 28 volt dc motor-operated butterfly valve. A manual override also functions as a position indicator.
E6/E9 Valve
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 A.  The E6/E9 valve controls flow of equipment cooling air to the E6 and E9 racks in the center equipment bay. The valve is a butterfly type valve actuated by a dual coil latching solenoid. The E6/E9 valve is powered by 28 volt dc from the 28 vdc MN BAT BUS. The valve has no manual override or exterior visual position indication.
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 21-58-00
 ALL  ú ú 01F Page 1 ú Feb 18/00
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

FORWARD EQUIPMENT COOLING 
EXHAUST COMPONENTS 
SEE  B 
FLIGHT DECK 
OVERHEAD PANEL 
DIFFERENTIAL 
PRESSURE SWITCH 
FLIGHT DECK 
LOW FLOW 
DETECTOR 

E/E RACKS
MAIN EQUIPMENT FORWARD EQUIPMENT COOLINGLOW FLOW DETECTOR
SUPPLY COMPONENTS SEE A
FORWARD EQUIPMENT COOLING SYSTEM
Equipment Cooling System - Component LocationFigure 1 (Sheet 1)
D11764
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 21-58-00
 ALL  ú ú 01F Page 2 ú Feb 10/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

CHECK VALVE 
TO FLIGHT DECK THREE-WAY VALVE  AIR CLEANER  OVERHEAT SWITCH  TO MAIN EQUIPMENT CENTER 
OVERHEAT SWITCH  SMOKE/OVERRIDE VALVE SUPPLY FAN 
SMOKE DETECTOR 
CONDITIONED AIR  AIR INLET  BYPASS VALVE  SKIN SWITCH TEMPERATURE FWD  TO E1/E2 
　
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