(2)
Operation
(a)
The axial flow fan is designed to operate at a nominal shaft speed of 11,500 revolutions per minute when supplied with aircraft electric power through the fan-mounted electrical connector. Current from the electrical connector is conducted through the leadwires to the stator assembly. The stator assembly induces the rotor to rotate, turning the impeller. The impeller causes air to flow through the axial flow fan. If the temperature of a winding reaches 400°F, an internal thermal switch deactivates the fan relay, shutting the fan off. When the winding temperature decreases to 340°F, the thermal switch resets, restoring the fan.
C. Aft Cargo Temperature Control Switch____________________________________
(1) The temperature control consists of a temperature sensor/switch which senses the cargo compartment temperatures. Whenever the cargo compartment is below 50°F the switch closes and a signal is sent to the fan and heater. When the cargo compartment air temperature reaches 70°F the switch interrupts power to the heater and fan.
D. Aft Cargo Fan Current Sensor or Current Sense Relay___________________________________________________
(1) AIRPLANES WITH THE AFT CARGO FAN CURRENT SENSOR; A fan current sensor is located on the right miscellaneous electrical panel, P37. The current sensor detects if the fan has electrical power. If the fan has a failure, the current sensor will provide a ground to the EICAS computers and the AFT CARGO FAN message will show.
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(2)
AIRPLANES WITH THE AFT CARGO FAN CURRENT SENSE RELAY; A fan current sense relay is located on the right miscellaneous electrical panel, P37. The relay detects if the fan has electrical power. If the fan has a failure, the relay will provide a ground to the EICAS computers and the AFT CARGO FAN message will show.
E.
Aft Cargo Heating Inlet Grill
_____________________________
(1) The grill in the front of the aft cargo compartment covers the inlet of the aft cargo heating system. It includes a wire filter to keep dirt and debris out of the aft cargo heater and the flow fan.
3. Operation (Fig. 2)
_________
A. Aft Cargo Heating
(1)
The aft cargo heating system is a self-contained system. The system uses a thermal switch for compartment temperature control and internal temperature sensors to prevent heater overheat.
(2)
If the cargo compartment temperature switch falls below 50°F (10°C) the temperature control switch closes, energizing the aft cargo fan relay and the aft cargo heater relay. The aft cargo heater heats the air. The aft cargo heat fan circulates air thru the heater and into the aft cargo compartment.
(3)
If the Cargo Compartment Switch reaches 70°F (21°C) the temperature control switch opens. The aft cargo heater shuts off immediately. The aft cargo heating fan stays on for 20 seconds and then shuts off.
(4)
If heater surface temperature exceeds 390°F (199°C) or if heater outlet temperature exceeds 180°F (82.2°C) the heater is de-energized. The heater is re-energized when surface temperature drops below 350°F (177°C) and heater outlet temperature drops below 160°F (71.1°C).
(5)
If the heating flow fan motor temperature reaches 400°F (204°C), the fan relay is deactivated and the fan and the heater shut off.
(6)
An EICAS status and maintenance message AFT CARGO FAN will appear when the temperature control switch is closed and the heating flow fan is not operating.
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MAINTENANCE MANUAL
G20728
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