Erratic Operation of HVAC System Test

Erratic operation of the A/C and heater systems including:
- Lack of cold air
- Lack of hot air
- Unrequested mode change (ATC only)
- No control of mode or temperature control or tapping blend door noise

These symptoms may be accompanied by the following Diagnostic Fault Codes (DTC's):
- Blend door feedback
- Blend door stall
- A/C Control Mode door input shorted to battery
- In-car temp sensor failure
- ATC messages not received
- Mode door stall

Check for the presence of DTC's with the DRB III(R). If the symptoms and or DTC's listed above are present, perform the following Repair Procedure:

With the vehicle at room temperature 10 to 27° C (50 to 80° F), pull the M-1 fuse for five minutes to erase any DTC's. Replace the fuse and start the vehicle to recalibrate the HVAC system. Operate the vehicle and A/C heater system to verify that symptoms and or DTC's are gone. If tapping noise or blend stall/feedback DTC's re-occur, additional diagnosis will be required.