Device for the regulation of a surface temperature level and for the prevention of icing-up of a heat pump evaporator for air conditioning units of vehicles, consisting of a segment of a refrigeration circuit that can be operated both as a heat pump and an air conditioning unit, comprising • the heat pump evaporator, which during operation as an air conditioning unit, in the direction of operation of the air conditioning unit, functions as an air conditioning unit condenser, • an adjustable expansion valve for opening and closing, • a refrigerant compressor, • refrigerant lines between the expansion valve and the heat pump evaporator and also between the heat pump evaporator and the refrigerant compressor, • a radiator fan, which is allocated to the heat pump evaporator, which withdraws by suction ambient air at an adjustable flow speed in front of and through the heat pump evaporator and hence permits a steady overflow of the heat pump evaporator surface with ambient air, • a first temperature sensor for detecting the temperature of the refrigerant and also • a control and regulation unit which, via signal lines (10, 10a, 10b, 10c, 10e) is at least connected to • the first temperature sensor, • further sensors, measurement signal generators or computer units with calculated values which are designed to detect the ambient air temperature (T u) and the vehicle speed (V F), • the expansion valve, • the radiator fan and • the refrigerant compressor, and has the technical programming means • for the analysis and processing of the measurement signals from the sensors (6, 7) connected to the control and regulation unit via signal lines (10, 10a), • for the regulation of the flow cross-section of the expansion valve and the refrigerant compressor as well as • for the activation of the radiator fan of the vehicle during operation as a heat pump, characterised in that • the first temperature sensor, in the direction of operation of the heat pump, is arranged in front of the heat pump evaporator and • for regulation of the exit temperature (T out) of the refrigerant from the heat pump evaporator, a pressure sensor or combined pressure-temperature sensor connected to the control and regulation unit via a signal line (10, 10d) is provided in the refrigerant line (5, 5b), in the direction of heat pump operation downstream of the exit of the heat pump evaporator on the way to the refrigerant compressor. • the heat pump evaporator, which during operation as an air conditioning unit, in the direction of operation of the air conditioning unit, functions as an air conditioning unit condenser, • an adjustable expansion valve for opening and closing, • a refrigerant compressor, • refrigerant lines between the expansion valve and the heat pump evaporator and also between the heat pump evaporator and the refrigerant compressor, • a radiator fan, which is allocated to the heat pump evaporator, which withdraws by suction ambient air at an adjustable flow speed in front of and through the heat pump evaporator and hence permits a steady overflow of the heat pump evaporator surface with ambient air, • a first temperature sensor for detecting the temperature of the refrigerant and also • a control and regulation unit which, via signal lines (10, 10a, 10b, 10c, 10e) is at least connected to • the first temperature sensor, • further sensors, measurement signal generators or computer units with calculated values which are designed to detect the ambient air temperature (T u) and the vehicle speed (V F), • the expansion valve, • the radiator fan and • the refrigerant compressor, and has the technical programming means • for the analysis and processing of the measurement signals from the sensors (6, 7) connected to the control and regulation unit via signal lines (10, 10a), • for the regulation of the flow cross-section of the expansion valve and the refrigerant compressor as well as • for the activation of the radiator fan of the vehicle during operation as a heat pump, • the first temperature sensor, • further sensors, measurement signal generators or computer units with calculated values which are designed to detect the ambient air temperature (T u) and the vehicle speed (V F), • the expansion valve, • the radiator fan and • the refrigerant compressor, • for the analysis and processing of the measurement signals from the sensors (6, 7) connected to the control and regulation unit via signal lines (10, 10a), • for the regulation of the flow cross-section of the expansion valve and the refrigerant compressor as well as • for the activation of the radiator fan of the vehicle during operation as a heat pump, • the first temperature sensor, in the direction of operation of the heat pump, is arranged in front of the heat pump evaporator and • for regulation of the exit temperature (T out) of the refrigerant from the heat pump evaporator, a pressure sensor or combined pressure-temperature sensor connected to the control and regulation unit via a signal line (10, 10d) is provided in the refrigerant line (5, 5b), in the direction of heat pump operation downstream of the exit of the heat pump evaporator on the way to the refrigerant compressor.