737 MAX Flight Crew Operations Manual
Air Systems -
Air Conditioning System
Description
2.30.6
MN-FLT-OH-201
Unbalanced Pack Temperature Control Mode
Any failure affecting the supply of trim air will cause the temperature control
system to control both packs independently. If flight deck trim air is lost, the left
pack will provide conditioned air to the flight deck at the selected temperature and
the right pack will satisfy the demand of the passenger zone which requires the
most cooling. If a passenger cabin zone trim air, or all trim air is lost, the forward
and aft zone temperature demands will be averaged for control of the right pack.
If any individual zone is transferred OFF, the Temperature Selector setting will be
ignored by the temperature control system.
Standby Pack Average Temperature
If all zone controls and primary pack controls fail, the standby pack controls
command the packs to produce air temperatures which will satisfy the average
temperature demand of the two cabin zones. The trim air modulating valves will
close. The flight deck zone Temperature Selector will have no effect on the
standby pack controls.
Fixed Cabin Temperature
If all Temperature Selectors are positioned OFF, the IASCs will cause the left pack
to maintain a fixed temperature of 75°F (24°C) and the right pack to maintain 65°F
(18°C) as measured at the pack temperature sensor.
Air Conditioning Distribution
Conditioned air is collected in the mix manifold. The temperature of the air is
directly related to the setting of the Temperature Selectors.
Overheat detection is provided by temperature sensors located downstream of the
packs and the mix manifold. An overheat condition causes the appropriate trim air
modulating valve to close and the ZONE TEMP light to illuminate.
Flight Deck
Since the flight deck requires only a fraction of the air supply provided by the left
pack, most of the left pack output is routed to the mix manifold.
Conditioned air for the flight deck branches into several risers which end at the
floor, ceiling and foot level outlets. Air diffusers on the floor under each seat
deliver continuous air flow as long as the manifold is pressurized.
Overhead diffusers are located on the flight deck ceiling, above and aft of the No.
3 windows. Each of these outlets can be opened or closed as desired by turning a
slotted adjusting screw.
March 1, 2021
