737 Flight Crew Operations Manual
Air Systems Chapter 2
Air Conditioning System Description Section 31
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
D6-27370-866-EGP 2.31.1
31 Air Conditioning System Descr iptionAir Conditioning System DescriptionFile Highlight
Introduction
The air conditioning system provides temperature controlled air by processing
bleed air from the engines, APU, or a ground air source in air conditioning packs.
Conditioned air from the left pack, upstream of the mix manifold, flows directly
to the flight deck. Excess air from the left pack, air from the right pack, and air
from the recirculation system is combined in the mix manifold. The mixed air is
then distributed through the left and right sidewall risers to the passenger cabin.
Conditioned air for the cabin comes from either the airplane air conditioning
system or a preconditioned ground source. Air from the preconditioned ground
source enters the air conditioning system through the mix manifold.
Air Conditioning Pack
The flow of bleed air from the main bleed air duct through each air conditioning
pack is controlled by the respective pack valve. Normally, the left pack uses bleed
air from engine No. 1 and the right pack uses bleed air from engine No. 2. A single
pack in high flow is capable of maintaining pressurization and acceptable
temperatures throughout the airplane up to the maximum certified ceiling.
The APU is capable of supplying bleed air for two packs on the ground, or one
pack in flight. Most external air carts are capable of supplying adequate bleed air
for two pack operation. Do not operate more than one pack from one engine.
Airflow Control
With both air conditioning pack switches in AUTO and both packs operating, the
packs provide “normal air flow”. However, with one pack not operating, the other
pack automatically switches to “high air flow” in order to maintain the necessary
ventilation rate. This automatic switching is inhibited when the airplane is on the
ground, or inflight with the flaps extended, to insure adequate engine power for
single engine operation. Automatic switching to “high air flow” occurs if both
engine bleed air switches are OFF and the APU bleed air switch is ON, regardless
of flap position, air/ground status or number of packs operating.
With the air conditioning pack switch in HIGH, the pack provides “high air flow”.
Additionally, an “APU high air flow” rate is available when the airplane is on the
ground, the APU bleed air switch is ON and either or both pack switches are
positioned to HIGH. This mode is designed to provide the maximum airflow when
the APU is the only source of bleed air.
March 25, 2010
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