EFFECTIVITY:
040-999
21-40-00 PAGE
21-40-00Jan1
PIPER AIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCEMANUAL
A. Heatingand Cooling (continued)
1. Fault Isolation (Environmental Control System) (continued)
CHART 1 FAULT ISOLATION (ENVIRONMENTALCONTROLSYSTEM) (Sheet 2 of 2)
Fault Cause Remedy
Insufficient conditioned airflow. Bleed air ON/OFF valve Check wiring.
not full open.
Leaks in jointsor connections. Repair leaking joints and
connections.
Cooling turbine rotating Replace cooling turbine.
torque unsatisfactory.
(See Note.)
Heat exchanger leaking. Replaceheat exchanger.
MalfunctioningVariable Removeand replace valve.
Ejector Mixing Valve
NOTE: Refer to label on cooling turbine for maximum acceptabletorque value.
EFFECTIVITY:
040-999
Jan 10/90 21-40-00
PIPER AIRCRAFT
PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL
A. HeatingandCooling(continued)
2. ComponentDetailedDescriptions
Thissystem,operated by enginebleed air, is controlled bya pressure regulatorandflowlimitingventuri,alongwith various componentswhichcomprise controlsystem.The
theenvironmental
followingisa description of these variouscomponents:
(a)
PressureRegulatingand Shutoff Valve Thepressureregulatingand shutoff valve is installed in the bleedair line upstream from the refrigerationunit. This is a solenoid operated valve whichregulatesthe bleed air supply pressure to the refrigerationunit and includesmeans for shuttingoff all bleed air to the refrigeration unit.
(b)
BleedAir Supply OverpressureSwitch Thisswitch,located at the inlet to the refrigeration unit,monitors bleed air pressure to the unit andsignalsthe regulating and shutoff valveto shut off air flow if pressure exceeds40 + 3 psig.
(c)
VariableEjector Mixing Valve The PA-42-720 usesa variable ejectormixing valve. The PT6A-61engineproducesa higher compressorbleedair pressure and a resulting higherbleedair temperature.The variable ejector mixing valve mixesthis higher press/temp. compressorbleed air with interstage turbine bleedair and controls both temperature and pressure of the bleed air supply.
(d)
PrimaryHeatExchanger Thisheat exchanger,locatedin the refrigerationunit,is used to lowerthe high bleedair temperatureprior to being routed to the compressor.
(e)
Compressor The compressor in the refrigerationunitis boot strappedto the turbineandcompressesthe bleedair to a higher pressure which raises the temperature.
(f)
CompressorDischargeOvertemperatureSensingSwitch Thisswitch, installedat the compressor dischargeport, senses discharge temperature. The switch,normallyclosed,must open when temperatures reach425°F ± 5°F and must signal the pressureregulatorand shutoff valveto close and shutoff the bleedair supply to the refrigerationunit.
(g)
SecondaryHeatExchanger Thisheat exchanger, located in the refrigeration unit, is used to lower the air temperature (still highdue to flow through the compressor).
(h)
CoolingTurbine Thecoolingturbine,installedon the common shaft with the compressor,receivesthe precooled air from the secondaryheatexchanger. This air, still at high pressurewhenpassing through the turbine, is lowered by expansion. The turbine absorbsenergyfromthe high pressure bleed air and drivesthe compressor. The expansion of the bleedair, plus its loss of energy, causes a temperaturereductionat the turbine discharge.
(i)
Mixing Muff Thismixingdevice,locatedimmediatelydownstreamfrom the cooling turbine(1) mixescold turbine outlet air with hot bleed air from the hot air bypass valve and (2) prevents icingof the turbine rotor and dischargeducting.
(j)
HotAir Bypass Valve Thisvalveis installed between the turbinemixing muff andthe bleed air line to the primaryheat exchanger. its function is to modulatethe flow of hot bleed air into the mixing muff accordingto signals sent to the valve from the cabin temperaturesensorand controller. This valveuse an electric actuator motor.
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