SECTION 22: HEATING AND AIR CONDITIONING
2
PA1621 Maintenance Manual All Series | Section Revised November 2017
4.9
SHUT‐OFFVALVEWITHSERVICEPORT........................................................................................................32
4.10 LIQUIDREFRIGERANTSOLENOIDVALVE.....................................................................................................32
4.10.1 Typicalmalfunctions............................................................................................................................32
4.10.2 ElectricalBypass/OnDemandOpeningofliquidrefrigerantsolenoidvalves......................................33
4.10.3 CoilReplacement.................................................................................................................................33
4.10.4 ValveDisassembly................................................................................................................................33
4.10.5 ValveReassembly................................................................................................................................33
4.11 THERMOSTATICEXPANSIONVALVE............................................................................................................34
4.11.1 CentralSystem.....................................................................................................................................34
4.11.2 SuperheatAdjustment.........................................................................................................................35
4.11.3 Maintenance........................................................................................................................................36
4.11.4 Driver’sUnit.........................................................................................................................................36
4.12 HOTWATERPNEUMATICVALVE.................................................................................................................36
4.12.1 ValveTroubleshooting.........................................................................................................................38
4.13 HOTWATERCIRCULATINGPUMP................................................................................................................38
4.13.1 CentralHVACsystem...........................................................................................................................38
4.13.2 SmallHVACsystem..............................................................................................................................39
4.13.3 Removal...............................................................................................................................................39
4.13.4 Installation...........................................................................................................................................39
5. HVACSYSTEMTESTINGANDTROUBLESHOOTING......................................................................................40
5.1 ONDEMANDDISPLAYOFA/CSYSTEMHIGHANDLOWSIDEPRESSURE....................................................40
5.2 ONDEMANDACTIVATIONOFHOTWATERCIRCULATINGPUMP...............................................................40
5.3 TEMPERATURESENSORS.............................................................................................................................41
5.4 TESTMODEFORSWITCHESANDSENSORS.................................................................................................41
5.5 TESTMODEFORELECTRICMOTORS...........................................................................................................42
5.6 MODESOFOPERATION...............................................................................................................................42
5.7 HVACELECTRICALSYSTEMTROUBLESHOOTING.........................................................................................43
5.7.1 AirConditioning...................................................................................................................................45
5.7.2 ExpansionValve...................................................................................................................................47
5.8 TEMPERATURES&PRESSURESCHART........................................................................................................48
5.9 LEAKTESTING...............................................................................................................................................48
6. CENTRALHVACSYSTEM.............................................................................................................................48
6.1 AIRCIRCULATIONINDRIVER’SAREA...........................................................................................................49
6.2 AIRCIRCULATIONINPASSENGER’SAREA....................................................................................................50
6.3 HVACSYSTEMOPERATION..........................................................................................................................51
6.3.1 ControlUnit..........................................................................................................................................51
6.3.2 OverheadCompartmentUnit..............................................................................................................51
6.4 HEATING......................................................................................................................................................52
6.4.1 Driver’sUnitHotWaterPneumaticValve............................................................................................52
6.4.2 Passenger’sUnitHotWaterPneumaticValve.....................................................................................52
6.4.3 DrainingHeatingSystem.....................................................................................................................52
6.4.4 FillingHeatingSystem..........................................................................................................................55
6.4.5 BleedingHeatingSystem.....................................................................................................................55
6.5 COOLING......................................................................................................................................................56
6.5.1 RefrigerationCycle...............................................................................................................................56
6.5.2 Refrigerant...........................................................................................................................................56
6.5.3 RefrigerantSystemClean‐outAfterCompressorFailure.....................................................................58
6.5.4 PumpingDown.....................................................................................................................................59
6.5.5 AddingVaporStateRefrigerant...........................................................................................................61
6.5.6 ChargingSystem..................................................................................................................................62
6.6 LIQUIDREFRIGERANTRECOVERY................................................................................................................63
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