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MAINTENANCE MANUAL
15. Overheat Switch
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A. The overheat switch mounts on the main equipment cooling supply duct just downstream of the air cleaner. The overheat switch closes when the duct temperature increases to 140°F (60°C). An overheat condition will generate the EICAS caution message, EQUIP COOLING and the EICAS status message, EQUIPMENT TEMP. With the air/ground system in the ground mode the gound crew warning horn will sound. The overheat switch will reopen when the temperature decreases to below 130°F (54°C).
16. Fan Current Sensor
__________________
A. A supply fan current sensor and an exhaust fan current sensor monitor current flow to the supply and exhaust fan. The P414 power distribution center houses the exhaust fan current sensor. The P415 power distribution center houses the supply fan current sensor.
17. Equipment Cooling Card
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A. The equipment cooling card monitors the position of system valves in relation to selected equipment cooling operating modes. If a valve is not in its commanded position the equipment cooling card transmits the information to the EICAS interface units via an ARINC 429 data bus. The applicable failure message will be displayed on the EICAS status page.
B. The equipment cooling card control output is limited to command of a clean cycle once every 10 decent detects. System valves and fans are commanded to the override mode for a length of two minutes.
C. The equipment cooling card is installed in the M7603 forward electrical systems card file.
18. Equipment Cooling Mode Select Switch
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A. The EQUIP COOLING mode select switch is located on the cabin temperature control module installed on the P5 overhead panel.
B. Equipment cooling automatic control is obtained with the mode selector switch in the normal (NORM) position. In addition there are two manual select backup modes, standby (STBY) and override (OVRD).
19. Operation (Figs. 2, 3)
_________
A. General
(1)
The equipment cooling control switch has three positions: NORM, STBY, and OVRD.
(2)
The NORM position is normally used for ground and flight operation.
(3)
The STBY position is used to close the ground exhaust valve if the NORM position fails to close the valve. When the cargo air conditioning system is operating, the STBY position will not close the ground exhaust valve.
(4)
The OVRD position is used for smoke evacuation in the equipment cooling system, or after a dual fan failure. This position is used only in flight.
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A 747-400 MAINTENANCE MANUAL
SKIN TEMPERATURE GROUND EXHAUST
CHECK VALVE
VALVE (REF) AFT EQUIPMENT COOLING
Equipment Cooling System - Schematic Figure 2
OPEN CLOSED
D11401
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MAINTENANCE MANUAL
MODE DESCRIPTION SUPPLY FAN FAN HAUST EX- VALVE IN-BOARD SUPPLY VALVE HAUST IN-EX-BOARD VALVE EX-GROUND HAUST VALVE BYPASS VALVE SMOKE/ OVRD VALVE E6/E9 _<1_>2 PACKS ON PACK ON 3-WAY * VALVE
1 GROUND -"NORM" ENGINES (7`C) OFF AMBIENT TEMP <45`F ON ON OPEN OPEN CLOSED CLOSED CLOSED OPEN AIR A/C AIR E/E
2 GROUND -(7`C) OFF AMBIENT "NORM" ENGINES TEMP >45`F ON ON OPEN CLOSED OPEN CLOSED CLOSED OPEN AIR A/C AIR E/E
3 GROUND -"NORM" ENGINES ON AMBIENT READY FOR FLIGHT ON ON OPEN OPEN CLOSED CLOSED CLOSED OPEN AIR A/C AIR E/E
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