PIPER AIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCE MANUAL
A. Distribution
Bleed air is ducted from the nacelle firewall to the ECU in the aircraft nose. The cooling air vent in the
wing root fairing provides a flow path overboard when a bleed coupling O-ring fails. The bleed mixing
capabilityof the bleed air control valve assumes a lower bleed air temperature in the ducting system
andeliminatesthe need for bleed ducting cooling flow.
After bleed air lines penetrate the fuselage on either side, they join at a Y-duct downstream from a
check valve installed in each leg of the Y. These check valves prevent reverseflow into a non-
operating engine or non-pressurized The duct
duct system and prevent loss of cabin pressurization. from the Y-duct forwardto the forward pressure bulkhead,fuselage station 57.00, is shrouded and vented overboard at the bottom of the fuselage, with the inlet in the right hand equipment compartment at fuselage station 57.00 bulkhead.
A ram air-bleed air intercooler is installed at the firewall to cool the bleed air supply auxiliary systems
below 250°F, prior to entering the fuel tank area aft of the firewall. When the ram air inlet to the
intercoolerisblocked,a bleed air overtemperature
switchis installed in the bleed air duct downstream of the intercooler. This switch is set to close at 425°F ±50F, which will illuminate the BLEED AIR HOT light on the pilot annunciator panel. If this occurs, the following steps must be taken:
1.
Shut off the ECU bleed air from that engine by using the ON-OFF switch on the overhead engine switch panel.
2.
If the light remains on after shutting off the ECU bleed air, the 425°F switch could have caused the light to illuminate. Since this air cannot be shut off, power to that engine must be reduced.
3.
If the light remains on after completing steps 1 and 2, make a precautionary landing as soon as practical, using minimum engine power on the affected side.
4.
Inspectengine bleed air duct system and make the necessary repairs.
The cabin air distribution systemuses bleed air from the engines and air entering the ECU from outside the airplane to operate the ECS. The ECS in turn produces cabin heating or cooling and air to defrost the windshield and side windows. Hot bleed air is used to supply heat, when required,through a bypass valve on the ECU. The bypass valve controls the amount of hot air mixedwith cold air prior to the air entering thecabin.
Air is distributedthrough out the cabin through a system of ducts, blower motors, louvers and outlets. The air boxes, located forward of the spar boxes, house blower motors which help distributethe proper volume of air to each outlet. A diverter valve, located below the junctionof the windshield and side window defroster lines, is installed to operate the distribution of defroster air for these windows.
The ECS cabin selector panel, located at the lower portion of the copilot's instrument panel, allows
for operation of cabin air distribution with the use of electrically operatedtemperatureand pressure
controls.
ABIN AIR
CABIN COMFORT
ECS SELECTOR
HEAT
HEAT
ECS SELECTORL
ECS Cabin Selector Panel Figure 1
EFFECTIVITY:
040-999
21 2000 JanPAGE
21-20-00Jan10/90
PIPER AIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCE MANUAL
A. Distribution (continued)
CREWFOOT FS WARMER
CREWANDPASSENGER 'OVERHEADAIR OUTLET (COLDAIR)
FROM -ECS
\ VALVE
WINDSHIELD DEFOG CONTROL VALVE
SIDE WINDOW | DEFOGOUTLET LJ
COLD AIR
' AAIRDIST SELECTOR 'OVHD' FANS'OFF'
DEFROSTERMAYBE SELECTED 'ON"OR'OFF'
Cabin Air DistributionSchematic-Conditioned Air Figure 2
EFFECTIVITY:
040-999
Jan 10/9021-20-00
Jan 10/90 =20' 00
PIPERAIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCEMANUAL
A. Distribution (continued)
CREWAND PASSENGER CREW FOOT
OVERHEADAIR OUTLET (COLD AIR) WARMER
FROM
ECS
WINDSHIELD
DEFOGCONTROL
VALVE
SIDE WINDOW
DEFOGOUTLET
WARMAIR
'AIRDIST SELECTOR "FLOOR"
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