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.
2.31.2 D6-27370-866-EGP
Ram Air System
The ram air system provides cooling air for the heat exchangers. Operation of the
system is automatically controlled by the packs through operation of ram air inlet
doors.
On the ground, or during slow flight with the flaps not fully retracted, the ram air
inlet doors move to the full open position for maximum cooling. In normal cruise,
the doors modulate between open and closed. A RAM DOOR FULL OPEN light
illuminates whenever a ram door is fully open.
Deflector doors are installed forward of the ram air inlet doors to prevent slush
ingestion prior to liftoff and after touchdown. Deflector doors extend when
activated electrically by the air–ground safety sensor.
Cooling Cycle
Flow through the cooling cycle starts with bleed air passing through a heat
exchanger for cooling. The air then flows to an air cycle machine for refrigeration.
The processed cold air is then combined with hot air which has bypassed the air
cycle machine, then through a high pressure water separator which removes
moisture. This conditioned air then flows into the mix manifold and distribution
system.
Overheat protection is provided by temperature sensors located in the cooling
cycle. An overheat condition causes the pack valve to close and the PACK light to
illuminate.
Pack Temperature Control
Electronic controllers command the pack temperature control valve toward open
or closed to satisfy pack discharge requirements.
If a primary pack control fails, the affected pack is controlled by the standby pack
control in the opposite controller. A primary or standby pack control failure causes
the PACK, MASTER CAUTION and AIR COND System Annunciator lights to
illuminate during recall.
If both the primary and the standby pack controls fail for the same pack, the
PACK, MASTER CAUTION, and AIR COND System Annunciator lights
illuminate. The pack will continue to operate without control unless excessive
temperatures cause the pack to trip off.
September 28, 2006
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