737 Flight Crew Operations Manual
Air Systems -
Air Conditioning System
Description
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
2.31.6 D6-27370-866-EGP
Recirculation Fan
The recirculation fan system reduces the air conditioning system pack load and the
engine bleed air demand. Air from the passenger cabin and electrical equipment
bay is drawn to the forward cargo bay where it is filtered and recirculated to the
mix manifold. The fans are driven by AC motors. Each recirculation fan operates
only if the respective RECIRC FAN Switch is selected to AUTO. In flight, the left
recirculation fan operates if both packs are operating unless either PACK switch
is in HIGH. The right recirculation fan operates in flight if both packs are
operating unless both PACK switches are in HIGH. On the ground, the left
recirculation fan operates unless both PACK switches are in HIGH and the right
recirculation fan operates even if both PACK switches are in HIGH.
Equipment Cooling
The equipment cooling system cools electronic equipment in the flight deck and
the E & E bay.
The equipment cooling system consists of a supply duct and an exhaust duct. Each
duct has a normal fan and an alternate fan. The supply duct supplies cool air to the
flight deck displays and electronic equipment in the E & E bay. The exhaust duct
collects and discards warm air from the flight deck displays, the overhead and aft
electronic panels, circuit breaker panels in the flight deck, and electronic
equipment in the E & E bay.
Loss of airflow due to failure of an equipment cooling fan results in illumination
of the related equipment cooling OFF light. Selecting the alternate fan should
restore airflow and extinguish the OFF light within approximately 5 seconds.
In the event of a forward cargo fire warning, the equipment cooling exhaust fan is
shut off and the equipment cooling exhaust OFF light is inhibited.
If an overtemperature occurs on the ground, alerting is provided through the crew
call horn in the nose wheel well.
Forward Cargo Compartment
The recirculation fan system circulates air from the passenger cabin around the
lining of the forward cargo compartment. When the overboard exhaust valve is
closed, exhaust air from the equipment cooling system is also diffused to the lining
of the forward cargo compartment for additional inflight heating.
Conditioned Air Source Connection
A ground air conditioning source may be connected to the mix manifold to
distribute preconditioned air throughout the airplane.
September 30, 2011
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