Heating and Ventilation Fault Diagnosis

This section covers mechanical, fuse and possible flap servo motor faults that could occur in the heating and ventilation system.

Visual checks of components within the system and relevant fuses should be carried out before undertaking detailed fault diagnosis procedures on Testbook.

Symptom - Heater Emits Cold Air Only, Driver Or Passenger Sides.

POSSIBLE CAUSE
- Engine running cold.
REMEDY
- See COOLING SYSTEM, Fault diagnosis.
POSSIBLE CAUSE
- Heater pipes or hoses blocked.
REMEDY
- Clear or renew heater pipes and hoses.
POSSIBLE CAUSE
- LH or RH temperature vent flaps in closed position due to inoperative servo motor.
REMEDY
- Renew servo motor.
POSSIBLE CAUSE
- Blown heating and ventilation system fuse.
REMEDY
- Check and renew fuses 8 or 17.

Symptom - Heater Emits Hot Air Only, Driver Or Passenger Sides.

POSSIBLE CAUSE
- LH or RH temperature vent flaps in open position due to inoperative servo motor.
REMEDY
- Renew servo motor.
POSSIBLE CAUSE
- Blown heating and ventilation system fuse
REMEDY
- Check and renew fuses 8 or 17.

Symptom - Heater Emits Hot or Cold Air To Demist Only.

POSSIBLE CAUSE
- Heater distribution vent flap locked in 'demist' position due to inoperative servo motor.
REMEDY
- Renew servo motor.
POSSIBLE CAUSE
- Blown heating and ventilation system fuse.
REMEDY
- Check and renew fuses 8 or 17.

Symptom - Heater Emits Hot or Cold Air To Footwell Only.

POSSIBLE CAUSE
- Heater distribution vent flap locked in 'footwell' position due to inoperative servo motor.
REMEDY
- Renew servo motor.
POSSIBLE CAUSE
- Blown heating and ventilation system fuse.
REMEDY
- Check and renew fuses 8 or 17.

Symptom - Heater emits hot or cold air to fascia vents only.

POSSIBLE CAUSE
- Heater distribution vent flap locked in 'fascia' position due to inoperative servo motor.
REMEDY
- Renew servo motor.
POSSIBLE CAUSE
- Blown heating and ventilation system fuse.
REMEDY
- Check and renew fuses 8 or 17.

Symptom - Heater Emits Hot or Cold Air To Fascia and Footwell Vents Only.

POSSIBLE CAUSE
- Heater distribution vent flap locked in 'fascia/footwell' position due to inoperative servo motor.
REMEDY
- Renew servo motor.
POSSIBLE CAUSE
- Blown heating and ventilation system fuse.
REMEDY
- Check and renew fuses 8 or 17.

Symptom - Heater Emits Recirculate Air Only.

POSSIBLE CAUSE
- Air inlet housing vent flap locked in closed 'recirculate' position due to inoperative servo motor.
REMEDY
- Renew servo motor.
POSSIBLE CAUSE
- Blown heating and ventilation system fuse.
REMEDY
- Check and renew fuses 8 or 17.

Symptom - Heater Emits Ambient Air Only

POSSIBLE CAUSE
- Air inlet housing vent flap locked in 'open' position due to inoperative servo motor.
REMEDY
- Renew servo motor.
POSSIBLE CAUSE
- Blown heating and ventilation system fuse.
REMEDY
- Check and renew fuses 8 or 17.

Symptom - No Boosted Air Supply To Heater Distribution Unit.

POSSIBLE CAUSE
- Blower motor(s) inoperative.
REMEDY
- Renew blower motor(s).
POSSIBLE CAUSE
- Blown motor fuse.
REMEDY
- Check and renew fuses 42 or 43.
POSSIBLE CAUSE
- Loose electrical connections.
REMEDY
- Check and tighten all relevant connections.

Symptom - Individual Heating and Ventilation Function/s Inoperative When Switch Control/s Are Used.

POSSIBLE CAUSE
- Switch function faulty.
REMEDY
- Renew switch control panel.
POSSIBLE CAUSE
- Switch control panel ECU faulty.
REMEDY
- Check and renew fuse 8 or fit new control panel.

Symptom - Heating and Ventilation System Inoperative.

POSSIBLE CAUSE
- Blown heating and ventilation system fuse.
REMEDY
- Check and renew fuses 8 or 17.
POSSIBLE CAUSE
- Switch control panel ECU faulty.
REMEDY
- Check and renew fuse 8 or fit new control panel.

Symptom - Poor Air Supply From Distribution Unit To Demist, Fascia or Footwell Vents.

POSSIBLE CAUSE
- Air distribution ducting leaking at joints or defective.
REMEDY
- Repair sealing joints or renew ducting.
POSSIBLE CAUSE
- Check through 1.1 - 12.1.
REMEDY
- Refer to 1.1 through to 12.1.


NOTE: Should any fault occur in the heating and ventilation system on vehicles fitted with air conditioning a 'book' and '!' symbol will be displayed on the switch control panel.