Contents Section: Heater All sections

Heater System Trouble Shooting GMC Cab & Chassis R2500

TROUBLE SHOOTING & DIAGNOSIS

ApplicationSpecification
Slow WarmingIncorrect operation of controls, Low coolant level, Control cables not attached, Blower motor not operating, Air doors not fully opening.
Exhaust Fumes In VehicleLeaking seal between engine compartment and plenum, Leaking seal between air inlet duct and dash.
Cold Drafts On FloorImproper operation of vent cables.
Insufficient Heat To Rear Seat AreaObstruction on floor.
Drop In Heater Air Temperature At Any Blower Motor SpeedLow engine coolant level, Air in cooling system.
Failure Of Cooling System To Warm UpIncorrect or inoperative engine thermostat.
No Coolant Flow Through Heater CoreKinked heater hoses, Plugged heater core, Inoperative water valve (auxiliary heater only).
Inadequate Removal Of Fog Or IceAir door not opening, Defroster door not opening, Temperature door not opening, Obstructions in defroster outlets at windshield, Dinged defroster outlets, Blower motor feed or ground disconnected, Blower motor or blower motor fuse inoperative, Inoperative blower motor switch.
Too Warm In VehicleTemperature door improperly adjusted, Incorrect operation of controls.
Blower Motor Not OperatingBlown fuse, Inoperative motor, Open circuit, Inoperative blower motor switch, Shorted or open blower resistor.

CONDITION & POSSIBLE CAUSE