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PIPER AIRCRAFT CORPORATION
SECTION 7
PA-31T2, CHEYENNE II XL
DESCRIPTION & OPERATION
7.37 CABIN AIR DISTRIBUTION SYSTEM
The cabin air distribution system, as shown in Figure 7-33, provides a
means of distributing the conditioned air from the ECS. The conditioned air
is routed from the water separator into an air distribution box attached to
the forward side of the forward pressure bulkhead. From the distribution
box, air is routed through the pressure bulkhead to the left and right side
vent panels and to the defroster vent system.
A fresh air duct and valve, are also incorporated in the distribution box.
The value is controlled by a push-pull cable connected to the cabin air
control lever located on the lower right of the instrument panel, next to the
windshield defog control. The fresh air valve can be opened by placing the
lever in the OUTSIDE position when the cabin is not pressurized. When
open, outside air is forced in from the entrance of the ram air cooling shroud
on the ECU, and distributed to the ducts in the cabin. During ground
operations, the PRESS position should be selected to prevent external
fumes from entering the cabin.
The left duct from the distribution box contains a duct overheat switch
and a recirculation switch. If the temperature in the duct gets too hot
(approximately 250°F), the ECS OVERTEMP light on the annunciator
panel will come on. If this warning light illuminates, the pilot should select
manual and momentarily hold the warm/ cool switch to the cool position to
reduce the duct temperature.
A recirculation switch controls the source doors located in the
recirculation fan boxes just forward of the spar. If the conditioned air
temperature rises to 100° F, the recirculation switch closes and positions the
air source valve to deliver air from the cabin floor to the cabin distribution
system. When conditioned air is below 70°F, the air source valve closes
causing cool air to be delivered to the overhead system.
Recirculation blowers feed the cabin distribution system through
sidewall plenums in the cabin. Branch ducting from these plenums connect
to cabin outlets which are individually adjustable. There is also a
conditioned air outlet in the instrument panel in front of the pilot and
copilot.
ISSUED: APRIL 22, 1981
REPORT: 2272
7-47
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