The invention relates to a device and a method for icing prevention regulation for a heat pump evaporator (3) in air conditioning systems of vehicles, composed of a subsection (1) of a refrigerant circuit which can be operated both as a heat pump and also as an air-conditioning system. The device comprises the heat pump evaporator (3), an electrical or mechanical refrigerant compressor (4), a cooler fan (9) which is assigned to the heat pump evaporator (3) and which draws ambient air (11) upstream of and through the heat pump evaporator (3) at an adjustable flow speed and which thus permits a permanent flow of ambient air (11) over the heat pump evaporator surface, a first temperature sensor (6) in or on the refrigerant line (5, 5a) upstream of the heat pump evaporator (3) with respect to the heat pump operating direction, and a control and regulating unit (8). The control and regulating unit (8) is connected via signal lines (10, 10a, 10b, 10c, 10e) at least to the first temperature sensor (6), to further sensors, in particular for detecting the ambient air temperature (Tu) and the vehicle speed (VF), to the expansion valve (2), to the cooler fan (9) and to the refrigerant compressor (4) for the direct or indirect regulation of the flow cross section of the expansion valve (2) and the rotational speed of the electric refrigerant compressor (4) or of the regulating valve of the mechanical refrigerant compressor (4) and for the actuation of the cooler fan (9) of the vehicle during heat pump operation.