夏延飞机维护手册 Cheyenne IIIA PA-42-720 AMM 1(56)

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systemto pressurizeafter takeoff.
Thecabinpressure controller is mounted on the lower center instrumentpanelandthe auxiliary volumetankand filter are located behind the instrument panel. The volume tankprovides additional volumeforthe rate pressurechamberin the controller to give greateraccuracyof the cabin rate-of-changecontrol. The air filter eliminatesentry of tobacco tar and dust particles greaterthan 0.3 micronsinto the pneumaticcontrolelementsof the controller.
The cabin outflowand safety valves,cabin absolute pressureswitches,cabindifferentialpressure switch,absolutepressureregulator,andvacuum relief solenoid valveare mounted on the aft pressure bulkhead.The vacuum regulatoris locatedbehindthe copilot's instrument panel. (Referto 37-00-00)
Thecabinair control, located directlyabovethe cabin comfortcontrols, has two positions marked
PRESSandOUTSIDE. When the control is in the PRESS position,the outside air inlet is closed and
the cabin can be pressurized. When the cabin air control is set to the OUTSIDE position, the outside
air inlet is open to allow freshair to be drawn into the cabinwhen the cabinis not pressurized.
A CABIN PRESS annunciator light on the annunciatorpanel warns the pilot if the cabin altitudegoes above11,500feet or if the cabin differential pressureexceeds6.45 psi. Cabinpressure is automaticallyregulatedto a maximum of 6.4 psi. If the cabin outflowvalve malfunctions, thecabin safety valve releases pressure. The CABIN PRESS/TEST/DUMPswitch is designed to prevent inadvertentdumpingof cabin pressure and must be pulled out before actuationto the DUMP or TEST positions.
EFFECTIVITY: 040-999
00PAGE
21-30-00 Jan10/90 1

PIPER AIRCRAFT
PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL

A. Pressurization Control (continued)
CHART 1 FAULT ISOLATION (PRESSURIZATION SYSTEM) (Sheet 1-of 5)
Fault
Cabin will not pressurize.
Cause

Blockedsafetyvalve cabin
air filter or orifice.
Blockedcontrollercabin air
filter with orifice.

Internalmalfunctionin the

isobaricvalve.
Internal malfunction in the
safetyvalve.

Internal malfunction in the

controller.
Defective"q"switch and/or
landing gear safety switch.

Defectivedump/testswitch. No pressure to door seal.
Excessiveleakage in pressurization
ducts. Excessivecabin leakage. Solenoid valve malfunctions
in the open position.
Valve on outside air control
box won't close.
Malfunction of ECS control
switch.
Malfunction of ECU pressure regulator and shut off valve.
Remedy
Replacefilter and check orifice.
Clean filter and check orificeon controller.
Removeand replace isobaric valve.
Removeandreplace safety valve.
Remove and replace controller.
Removeand replace switch.
Replaceswitch.
Check and repair door
sealor door seal valve. Locateleakand tighten
connections. Locateand repair leak.
Replacevalve.
Adjust or lubricate valve or control linkage.
Repairor replace switch.
Repairor replace valve.
EFFECTIVITY:
040-999

2
PAGE 1-30-00

Jan10/90 21-30
PIPER AIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCE MANUAL

A. PressurizationControl(continued)
CHART 1 FAULT ISOLATION (PRESSURIZATION SYSTEM)
Fault  Cause 
Cabinpressurizesto full  Vacuumtube not connected 
positivedifferential  to controller. 
pressureafter takeoff. 
Malfunctionin aircraft 
vacuumsupply. 
Rupturein volume tank. 
Internal malfunction inthe 
outflowisobaricvalve. 
Internalmalfunctionin the 
controller. 
Cabinaltitudedecreases below selected altitude.  Low aircraft vacuumsupply. 
Minorleak in tube between 
controllerand volume tank 
or in volume tank. 
Minorleak in tubebetween 
controller and isobaric valve 
or in isobaric valve. 
Minorleak in the controller. 

Minimumratesunbalanced. Minor leak in tube between Downrate faster than up controllerand volume tank rate. or in volume tank.
Minorleak in the controller.

Pressurizedoperation Solenoidvalve malfunction beforetakeoff and in the closed position. after landing.
"q" switch, landing gear squat switch or test/dump switchmalfunctionin the open position.
(Sheet 2 of 5)
Remedy
Connectvacuum tube.
Checkaircraft vacuum
supply.
Replace tank.
Removeand replace valve.
Removeand replace controller.
Checkaircraftvacuum supply.
Removeand replace tube or volume tank.
Remove and replacetube or isobaric valve.
　
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