737 MAX Flight Crew Operations Manual
Air Systems -
Air Conditioning System
Description
MN-FLT-OH-201
2.30.5
Zone Temperature Control
There are three zones: flight deck, forward cabin and aft cabin. Desired zone
temperature is set by adjusting the individual Temperature Selectors. The selector
range is approximately 65°F (18°C) to 85°F (30°C).
The packs produce an air temperature that satisfies the zone which requires the
most cooling. Zone temperature is controlled by introducing the proper amount of
trim air to the zone supply ducts. The quantity of trim air is regulated by individual
trim air modulating valves.
During single pack operation with the TRIM AIR selected ON, zone temperature
is controlled the same as during two pack operation. During single pack operation
with the TRIM AIR selected OFF, the pack attempts to produce an air temperature
to satisfy the average temperature demands of all three zones.
If air in a zone supply duct overheats, the associated amber ZONE TEMP light
illuminates, and the associated trim air modulating valve closes. The trim air
modulating valve may be reopened after the duct has cooled by pushing the TRIP
RESET Switch.
Zone Temperature Control Modes
The right IASC provides primary control for the flight deck (CONT CAB) and the
forward passenger cabin zone (FWD CAB). The left IASC provides primary
control for the aft passenger cabin zone (AFT CAB) and standby control for the
flight deck.
Failure of the right IASC will cause an automatic transfer of control to the left
IASC, providing normal temperature control for the flight deck using the CONT
CAB temperature selector. The FWD CAB and AFT CAB temperature selectors
will operate normally, but the temperature selector settings of the two passenger
cabins will be averaged.
Failure of the left IASC will allow the CONT CAB temperature selector to operate
normally. The FDW CAB and AFT CAB temperature selectors will also operate
normally, but the two temperature settings will be averaged.
Failure of the forward or aft cabin temperature control will cause the associated
trim air modulating valve to close. The temperature selectors will operate
normally, but the temperature selector settings of the two passenger cabin zones
will be averaged. The MAINT, MASTER CAUTION and OVERHEAD System
Annunciator lights will illuminate after landing to indicate failure of the
associated zone control.
Failure of both the right IASC and the left IASC will illuminate the MASTER
CAUTION light, the AIR COND system annunciator light and all three ZONE
TEMP lights.
March 1, 2021
