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INBOARD BODY LDG GEAR WHEEL WELL BULKHEAD (REF)
OVERRIDE
VALVE
A
747-400 MAINTENANCE MANUAL
SEE A TEMPERATURE SELECTOR SWITCH
FWD
SEE B
A
AFT CARGO TRIM VALVES (REF)
PNEUMATIC DUCT
FWDCONTROL VALVE
B
Aft Cargo Compartment Heating - Component Location
Figure 1 (Sheet 1)
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A
747-400
MAINTENANCE MANUAL
Aft Cargo Compartment Heating - Component Location
Figure 1 (Sheet 2)
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A
747-400
MAINTENANCE MANUAL
HEAT OUTLET HOLES
HEAT
OUTLET HOLES AFT CARGO HEAT DUCT
D
HEAT DUCT
Aft Cargo Compartment Heating - Component Location
Figure 1 (Sheet 3)
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G08715
A
747-400
MAINTENANCE MANUAL
PNEUMATIC MANIFOLD CROSSOVER DUCT
Aft Cargo Compartment Heating System Flow Diagram
Figure 2
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A
747-400
MAINTENANCE MANUAL
B. The aft cargo underfloor heat control switch is installed on the Sta 1940 body frame approximately 3 feet right of airplane centerline. The underfloor heat control switch is identical to the sidewall mounted switches.
C. The switch set points are as follows:
SWITCH______ OPEN TEMPERATURE________________ CLOSE TEMPERATURE Low Temperature 50°F (10°C) max 40°F (4°C) min High Temperature 60°F (16°C) max 50°F (10°C) min Overheat 80°F (26°C) min 90°F (32°C) max Underfloor Control 42°F (6°C) max 32°F (0°C) min
4. Aft Cargo Heat Switch_____________________
A. There is an alternate action switch/light labled AFT CARGO HEAT on the pilots' P5 overhead panel. The upper half of the switch indicates when the switch is set to ON. The lower half of the switch indicates TEMP when the overheat valve closes.
5. Temperature Selector Switch___________________________
A. The temperature selector switch is a two-position toggle switch located on the light switch panel just forward of the bulk cargo door. The switch sets compartment temperature by closing an electrical circuit through either the low or high temperature control switch.
6. Heat Duct_________
A. A heat duct is installed below the floor in the aft cargo compartments. Holes in the top of the duct supply warm air to the aft cargo compartments.
7. Operation_________
A. Functional Description (Fig. 3)
(1)
With the AFT CARGO HT switch set to ON and compartment temperature less than the selected temperature, power to the control valve is through the applicable temperature control switch. The system supplies heat until compartment temperature reaches the temperature control switch maximum limit. At this time, the temperature control switch opens, de-energizing a relay that switches power to close the control valve. The switch remains open until compartment temperature drops to the temperature control switch minimum limit. At this point the switch closes, energizing its relay and switching power to open the control valve.
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