Packs, Ram Air System, Recirc Fan and Air Flow are covered in the Bleed Air
Module.
Air Mix Valves and Temperature Controller
The two air mix valves for each pack control hot and cold air according to the setting of the
CONT CABIN or PASS CABIN temperature selector. Air that flows through the cold air mix
valve is processed through a cooling cycle and then combined with hot air flowing from the
hot air mix valve. In the automatic temperature mode, the air mix valves are operated by
the automatic temperature controller. The automatic temperature controller uses inputs
from the respective temperature selector and cabin temperature sensor. The automatic
temperature controller is bypassed when the temperature selector is positioned to
MANUAL. Anytime the pack valve closes, the air mix valves are driven to the full cold
position automatically. This aids startup of the cooling cycle and prevents nuisance hot air
trips when the pack is turned on.
Air Conditioning Distribution
Conditioned air is collected in the mix manifold. The temperature of the air is directly related
to the setting of the CONT CABIN and PASS CABIN temperature selectors. Overheat
detection is provided by temperature sensors located downstream of the packs. An
overheat condition causes the appropriate mix valves to drive full cold and the DUCT
OVERHEAT light to illuminate. A temperature higher than the duct overheat causes the
appropriate pack valve to close and the PACK TRIP OFF light to illuminate.
