The IHKR control unit is set into operation when the ignition is switched on. The IHKR is switched on by turning the blower control wheel out of the zero position. The air flow is set by further turning the blower control wheel up to stage 4, stage 5 then corresponds to the defrost setting. The blower motor is activated by means of a resistor circuit.
An increase in the set air flow rate due to the driving wind is essentially compensated by the fresh air flap closing dependent on the vehicle speed.