AIR CONDITIONING -RECIRCULATION -FUNCTIONAL DESCRIPTION

Functional Description -Normal
When the two recirculation fan switches on the P5 are ON, the OPAS sends signals to the CTCs. This sets the fans for automatic operation. The right CTC is the primary controller for the recirculation fans. If both channels of the right CTC fail, the left CTC controls the fans.
The CTC sends fan on signals to the ELMS electronic units (EEUs) in the left and right power management panels. The EEUs supply grounds to energize the recirculation fan relays. The relays supply power to each recirculation fan. The CTC turns the fans on and off with a 5 second delay between fans. This helps prevent a sudden load.
Functional Description -Overheat
The ECSMCs monitor overheat switches in the recirculation fans. The left ECSMC monitors the left lower and forward upper fans. The right ECSMC monitors the right lower and aft upper fans (not shown). If an overheat switch opens, the ECSMC sends an overheat signal to the CTC. The CTC latches the fan off. The CTC also latches the related fans off if there is a loss of data from an ECSMC.
Operation -Normal
The lower and upper recirculation fan switches are alternate-action switches. When the switches are off, the recirculation fans are off. When the switches are on, operation of the recirculation fans is automatic.
The upper and lower fans usually operate continuously on the ground and in flight. Single pack ground operation with high ambient temperature may cause a lower fan to stop. The CTC turns off the fan on the same side as the unserviceable pack. This decreases the amount of warm air put into the mix manifold and helps cool the airplane.
See the pack cooling and mix manifold temperature control section for more information (SECTION 21-52).
Operation -Non-normal
If the forward or aft cargo fire arm switches are in the ARMED position, the ELMS and the CTC turn off the lower fans.
If an upper or lower fan has a failure and pack flow schedule 1 is in effect, the pack flow rate increases 67 lbs/min (33.5 lbs/min per pack). This keeps the total cabin ventilation rate constant. The increased bleed air flow causes a small increase in fuel consumption, approximately .3% for each failed fan.
A status message shows if a recirculation fan has a failure. If the fan latches off because of an overheat condition, you can cycle the recirculation fan switch OFF then ON to release the latch. You can also use the AIR COND RESET switch to release the latch.
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AIR CONDITIONING -RECIRCULATION -FUNCTIONAL DESCRIPTION

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777 AIRCRAFT MAINTENANCE MANUAL

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AIR CONDITIONING -VENTILATION -GENERAL DESCRIPTION -MECHANICAL

Purpose
The ventilation system has these functions:
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Removes odors from the lavatories and galleys

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Causes air flow across the zone temperature sensors for the flight, passenger, and cargo compartments

*
Causes air flow through electrical and electronic equipment

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Removes warm air from above the passenger compartment ceiling and from the galley chiller units in the forward part of the airplane

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Supplies air flow into the bulk cargo compartment.

These are the types of ventilation:
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Galley chiller unit ventilation

*
Bulk cargo ventilation

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Lavatory/galley ventilation.

Galley Chiller Unit Ventilation
The chiller boost fan removes warm air from galley chillers and the area above the passenger compartment ceiling. Only chillers in the passenger compartment ceiling area above the galleys and forward of the wings connect to the fan.
The air from the chiller boost fan goes to the mix bay area. The lower recirculation fans (not shown) move the air from the mix bay into the mix manifold part of the air conditioning distribution system.
Holes in the duct let hot air from the chiller exhaust go into the ceiling when the fan is off.
The chiller boost fan operates automatically.
Bulk Cargo Ventilation
The bulk cargo ventilation fan increases the ventilation when there are animals in the bulk cargo compartment. The fan pulls air from the passenger compartment and moves it into the bulk cargo compartment. The fan operates when the bulk cargo heating system is set to HIGH.
Lavatory/Galley Ventilation
There are two lavatory/galley ventilation fans. Only one fan operates at a time. The right fan is primary and the left fan is the backup. At airplane power up, the left fan comes on, does a test, and goes off. The right fan then comes on, does a test, and stays on. The fan that operates pulls air from these areas and components:
　
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