An electric auxiliary heating unit reliably avoids temperature overshoots of the heated air. To this end, the temperature of the air flowing into the heating is determined and converted into a heating power for controlling the heating elements. This is preferably done via a stored characteristic field via which a plurality of vehicle parameters, such as the vehicle speed, the opening condition of the convertible top, etc., can be taken into account. Also the temperature of the incoming air can be derived from temperature values which are already available in the vehicle. A user-friendly electric heating can be realized very easily in this way. Temperature fluctuations in the heated air can be avoided reliably and easily even in the case of dynamically varying operating conditions of the motor vehicle.