Cabin Air Distribution Schematic-Heated Air Figure 3
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PIPER AIRCRAFT
PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL
A. Distribution(continued)
7
11
16 11
1.
Fresh Air Valve
2.
DegogVent Valve
3.
ConditionedAir Duct
4.
Crossover Duct
5.
Footwarmerand Side Window Defog Duct
6.
Heat Duct Plenum
7.
Defog Duct
8.
SideWindow Defog Outlet
9.
Overhead Air Outlets
10.
Defog Outlet
11.
12.
13.
14.
15.
16.
17.
18.
19.
20
Footwarmer Plenum Crew Side Outlet Filtered Recirculated Air Inlet Cabin Air Lever WindshieldDefog Lever Duct Temperature Sensor Recirculation Cut Switch OvertemperatureLight Switch Cabin Air Distribution Box and Blower Housing Cabin Heat Duct
Air Distribution System
Figure 4
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PIPERAIRCRAFT
PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL
A. Distribution(continued)
5. Removalof GroundCoolingFan
(a)
Gainaccessto baggage compartmentarea and removehardwaresecuring partition between baggagecompartmentandfan.
(b)
Removeaccesspanel on right side of nose section.
(c)
Loosenand removeclampssecuringfan to flexiblerubbercuffsand refrigerationunit.
(d)
Disconnectelectricalleadsto fan motor.
(e)
Slidecuffsfrom refrigeration unitso fan motor canbe removedfromrefrigerationunit.
(f)
Removefan.
6. Installationof GroundCoolingFan
(a)
Withfan in position,sliderubber cuffs overendsof fan.
(b)
Connectelectricalleads to fan motor.
(c)
Tightenclampssecuringfan in position.
(d)
Replaceaccesspanel removed fromright side of nose section.
(e)
Replacepartitionremovedfrom baggage compartment.
7. Removal of Check Valve Assembly
(a)
Removeclampssecuringhose between waterseparatorandcheck valve assembly.
(b)
Removebolts and washers that attach checkvalve to pressure bulkhead.
(c)
Removecheckvalve with gasket.
8. Installationof Check Valve Assembly
(a)
Install new valve and gasket to pressurebulkhead.
NOTE:Checkvalvemustbe installed with flapper shaft in verticalposition.
(b)
Securevalve in position withwashersand bolts.
(c)
Installhosebetweenwaterseparatorandcheckvalve.
(d)
Securehose with clamps.
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PIPERAIRCRAFT
PA-42-720(Advanced Trainer)
MAINTENANCE MANUAL
A. PressurizationControl
Pressurizedair for the airplane cabin is obtainedby mixing low pressure and high pressurebleedair from the engine compressor.Thebleed air is controlled by a solenoidshutoffvalve,operated by an ON-OFF switch on the overheadengineswitch panel. Thisbleed air is routed throughshrouded annular ducts, check valvesand insulated ducts to the inlet of the ECU, whichconditionsthe bleed air.
Thecabinpressurecontrol system consistsof the cabinoutflow valve, cabin safetyvalve,cabin
pressurecontroller,auxiliary volume tank, absolute pressureregulator,filter, vacuum solenoidrelief
valve,vacuumregulator,manualtestvalve, cabin pressure test/dumpswitch,cabin differential
pressureswitch,cabinabsolutepressureswitches, plumbing andwiring. Theseitems are given a
detailedoperationaldescriptionlater in this chapter.
Thecabin safety valveis left open on the ground with enginesoperatedby a vacuum applied to the
control chamber of the safetyvalve. The vacuum regulator of the vacuumsystemprovidesa vacuum
of 4.0 to 6.0 inches of mercury, referencedto cabin pressure. Enginebleedair is supplied to the
ejectorto produce the required vacuum. Thisvacuumholds the safetyvalve open while on the ground
throughthe action of the landinggear squat switch and "q" sensorsystemwhich energizes and opens
the vacuumrelief solenoid valve. The cabin pressurecontrolswitch on the lower center instrument
panelcontrolsthe vacuum reliefsolenoid valve. Whenplacedin the DUMP positionit energizes the
vacuum solenoid and opens the safety valve. TheTEST position, (FOR TEST PURPOSESONLY),
bypasses the safetyswitchon the left main landing gear and "q" sensorsystems,whichpreventsthe
cabin from pressurizing on the ground. The normal positionis CABIN PRESS, which allows the
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