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.
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.
