1. Using a compatible scan tool, check for fault codes in the control head.

2. Make sure the evaporator temperature sensor is reading correct temperature of the evaporator core.

3. Shorted wiring for actuators or faulty actuators can cause your condition.

4. Perform a system recalibration using a compatible scan tool. If the recalibration does not complete, try lowering the system voltage down to under 10 volts. Leave headlights or other load on and monitor battery voltage until below 10 volts (the battery will need to be recharged with a battery charger of alternator damage will result.). Then retry the calibration procedure. Some control heads do not run the calibration under normal system voltage values.

5. If all else fails, disconnect the battery cables and hold them together for one full minute. After reconnecting the battery cables, monitor the mode and temperature door operations at key on. Do Not Touch the a/c controls. The door should and go full travel. Turn the ignition off for at least 10 seconds but no longer than 30 seconds. Start the engine and see if the fault is cleared. Keep in mind that all learned memory will be cleared so the radio presets and clock will have to be adjusted. Also the engine idle may be erratic and cause a stalling condition. If so the throttle body will need to be cleaned using the appropriate cleaners and techniques.