Stepper Motors

On the automatic system, separate stepper motors operate the right-hand (RH) and the left-hand (LH) side temperature blend doors. On the manual system, a single stepper motor operates both the right-hand (RH) and the left-hand (LH) temperature blend doors.

The distribution doors in the heater are also operated by stepper motors. One for the windshield distribution door and one for the face and feet distribution door.

If a stepper motor is to be replaced, ensure it is replaced with the correct replacement part. Although similar in appearance, each of the stepper motors is different and faults will occur if an incorrect motor is fitted.

Operation of the distribution and temperature blend door stepper motors is controlled by the automatic temperature control (ATC) module, which is connected to the stepper motors by a LIN (local interconnect network) bus.

All of the stepper motors contain microprocessors, which store positional information. To enable the automatic temperature control (ATC) module to move the stepper motors correctly it requires the following information:

• The travel range, end to end, of each motor.
• Where each motor is on its range.

Approximately 2 minutes after the vehicle ignition is switched off, the climate control system powers down. At this point, the automatic temperature control (ATC) module stores the position of each stepper motor in its memory. Each of the stepper motors also stores its own position in its memory. When the ignition is next switched on, all of the stepper motors send positional information to the automatic temperature control (ATC) module via the LIN bus. This information is compared with the positional information stored within the automatic temperature control (ATC) module memory.

In normal circumstances, the information sent by the stepper motors matches that held in the automatic temperature control (ATC) module memory. In this instance, the automatic temperature control (ATC) module recognizes there are no problems with the system and starts normally. If however, there are differences, the automatic temperature control (ATC) module carries out a calibration routine.

The stepper motor calibration routine will normally take about 15 seconds to complete, but can take up to approximately 2 minutes in certain circumstances. During this period:

• The programmed de-frost light emitting diode (LED) on the automatic temperature control (ATC) module panel will flash.
• All other climate control operations will be suspended.

The programmed de-frost light emitting diode (LED) will stop flashing after 2 minutes, regardless of whether the exercise was successful or not so it is important to check that calibration has been carried out successfully. To do this:

1. Switch the ignition off.
2. Switch the ignition back on.
3. Check for a flashing programmed de-frost light emitting diode (LED).

If calibration has been successful, the programmed de-frost light emitting diode (LED) will not flash and the system will return to normal operation. If flashing does occur, more investigation will be required.

Automatic Calibration:  The automatic temperature control (ATC) module will automatically initiate a calibration routine every 175 hours of vehicle life. This occurs approximately 1 minute after the ignition has been switched off once 175 hours is reached. In this instance, the programmed de-frost light emitting diode (LED) will not blink.

Forced Calibration:  The automatic temperature control (ATC) module can be manually forced to carry out a calibration routine on the stepper motors. This can be carried out by holding down the ECON and recirculation buttons on the automatic temperature control (ATC) module panel while simultaneously switching the ignition on. The automatic temperature control (ATC) module will now carry out a calibration routine on the stepper motors, but will flash the ECON light emitting diode (LED) rather than the programmed de-frost light emitting diode (LED).