The electrical auxiliary heater heats up the heating air by means of electrical heating elements. It means there is always sufficient heat output available despite low lost heat at high levels of engine efficiency. The heat power request comes from the heater/air conditioning system (IHKA) via the junction box.
The electrical auxiliary heater and its control unit are components of the heat exchanger for the heating system in the air-conditioning system. The refrigerant-cooled heater fins have been supplemented by electrically heated heat exchanger elements made of ceramics.
The heating elements only cut in when there are sufficient electrical power reserves. The DDE control unit determines the present reserves of power in the vehicle electrical system. The DDE control unit informs the control unit of the electrical auxiliary heater by means of a PWM signal of the maximum additional electrical power.
The electrical auxiliary heater has a self-diagnosis function, but no fault code memory of its own. All faults are stored in DDE control unit.