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 switched 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 pack controls 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.
