more detail below in order to detect the thermal load on the system a temperature sensor 2 a and a sensor for the relative air humidity 2 b are arranged in the fresh air stream in the vicinity of the fresh air flap 2 a temperature sensor 3 a and a further sensor for the relative air humidity 3 b are arranged in the vicinity of the circulating air flap 3 the signals from the temperature sensors 2 a 3 a and from the air humidity sensors 2 b 3 b are supplied to the air condition regulator 7 for calculating the specific enthalpies for the fresh air and the circulating air the air condition regulator 7 opening and closing the fresh air flap 2 and the circulating air flap 3 as a function of these signals in such a way that the lowest enthalpy difference is set at the evaporator 6 the refrigerant circuit according to the invention will now be explained with reference to fig2 as already explained the mixed air 5 appearing downstream of the fan 4 is supplied to the evaporator 6 in the cooling mode this evaporator 6 is cooled with the aid of a refrigerant circuit 15 so that the air emerging into the passenger compartment interior acquires.