Packs, Ram Air System, Recirc Fan and Air Flow are covered in the Bleed Air
Module.
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 left electronic controller controls the aft cabin zone and provides backup control for the
flight deck. The right controller controls the forward cabin zone and provides primary
control for the flight deck. Failure of the primary flight deck temperature control will cause
an automatic switch to the back up control and will illuminate the CONT CAB amber ZONE
TEMP light upon Master Caution Recall. Failure of both the primary and standby controls
will illuminate the lights automatically. Failure of the forward or aft cabin temperature control
will cause the associated trim air modulating valve to close. The Temperature Selectors
operate normally, but the Temperature Selector settings of the two passenger cabin zones
will be averaged. The amber ZONE TEMP light will illuminate upon Master Caution Recall to
indicate failure of the associated zone control.
