21-25-00
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL
Left Recirculation Fan Operation Schematic
Figure 3
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21-25-00
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL
A. Functional Description______________________
(1)
Right Recirculation Airflow
(a)
Conditioned air from the passenger cabin is drawn through the return air grilles in the passenger cabin floor, into the sidewalls of the forward cargo compartment. The air is then drawn through the pre-filter and HEP filter. The filters clean the air of debris, smoke, and odors, before the air passes through the recirculation fan. The air is then blown through the right check valve and into the mix manifold.
(2)
Left Recirculation Airflow
(a)
Air is drawn from the flight deck, through the main panels, overhead panels, and the center aisle stand. This air is combined with air that is drawn through the weather radar and forward E/E racks. The air is then drawn through the left fan to be blown through the check valve and filter, into the mix manifold.
(3)
In the mix manifold, air from the left and right recirculation systems is combined with fresh conditioned air from the cooling packs. This air is redistributed to the passenger cabin by way of overhead ducting.
B. Recirculation System Operation______________________________
(1)
Right System
(a)
The right recirculation fan runs when the Right Recirculation Fan Relay is energized. The relay is energized when the R RECIRC FAN switch/light is ON, the FWD and AFT CARGO FIRE switches are unarmed, the Forward Supply Smoke Relay is relaxed, and the Right Recirculation Fan Thermal Switches are closed. When these conditions are met, the fan relay energizes, providing 115v ac power through its contacts, to operate the right recirculation fan.
(b)
When the right fan relay is relaxed, the right pack is commanded into high flow mode (Ref 21-51-00).
(2)
Left System
(a)
The left recirculation fan operates when the Left Recirculation Fan Relay is energized. 1) Left Recirculation Fan Operation on the Ground:
a) The fan relay is energized on the ground when the L RECIRC FAN switch/light is ON, the FWD CARGO FIRE switch is unarmed, and the Left Recirculation Fan Thermal Switches are closed.
2) Left Recirculation Fan Operation in the Air:
a) The fan relay is energized in the air when the L RECIRC FAN switch/light is ON, the FWD CARGO FIRE switch is unarmed, the slats are retracted, the Exhaust and Supply Smoke Sensing Relays are relaxed, no smoke is sensed in the forward supply equipment cooling system, and the Left Recirculation Fan Thermal Switches are closed.
b) If the slats are extended, the fan relay will be energized independent of the position of the exhaust and supply smoke sensing relays.
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757 MAINTENANCE MANUAL
3) When the left fan relay is energized, 115v ac power is supplied for the operation of the left recirculation fan.
4) When the left recirculation fan relay is relaxed, the left pack is commanded into high flow mode (Ref 21-51-00). In addition, if the airplane is in the air, the overboard exhaust valve is commanded to SMOKE (Ref 21-58-00).
C. Control_______
(1)
Two alternate action switch/lights, on the pilots' overhead P5 panel, control operation of the the recirculation air fans. A white ON light illuminates whenever the recirculation fan switch/light is selected ON, regardless of the operation of the fan. Depressing the switch/light again extinguishes the ON light.
(2)
To operate the system:
(a)
Provide electrical power (Ref 24-22-00).
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