Method for controlling an expansion valve of a refrigerant circuit comprising at least one evaporator , at least one internal heat exchanger , at least one compressor , at least one condenser , the expansion valve and a control device , connected to the expansion valve in a signal-conducting manner, for controlling the expansion valve , wherein a first fluid line of the at least one internal heat exchanger is arranged between the at least one condenser and the expansion valve and a second fluid line of the at least one internal heat exchanger is arranged between the at least one evaporator and the at least one compressor , wherein a refrigerant (K) circulates in the refrigerant circuit , wherein the refrigerant (K) flows, in a circulation direction (Z) of the refrigerant circuit starting from a valve outlet of the expansion valve , through the at least one evaporator , the second fluid line of the at least one internal heat exchanger , the at least one compressor , the at least one condenser , the first fluid line of the at least one internal heat exchanger and the expansion valve , wherein the refrigerant (K) is at least partially evaporated in the at least one evaporator through the input of heat into the refrigerant (K) by a heat source acting on the at least one evaporator , wherein the refrigerant (K) flowing through the first fluid line releases heat to the refrigerant (K) flowing through the second fluid line and the enthalpy of the refrigerant (K) is thus increased before entry into the at least one compressor , characterized in that the expansion valve is controlled in dependence on a temperature difference between a heat source temperature of the heat source and the evaporation temperature of the refrigerant (K), which prevails in the region between valve outlet of the expansion valve and compressor inlet of the at least one compressor , wherein the heat source temperature of the heat source acting on the at least one evaporator and the evaporation temperature of the refrigerant (K) are determined in the region between valve outlet and compressor inlet , wherein an actual heat source temperature difference (IW) is determined from the temperature difference between heat source temperature and evaporation temperature, wherein the actual heat source temperature difference (IW) is adjusted to a predefined or predefinable target heat source temperature difference (SW) by controlling an opening width of the expansion valve , wherein the target heat source temperature difference (SW) is continuously adjusted, wherein the control device comprises a further control mechanism for preventing the entry of liquid refrigerant (K) into the at least one compressor , wherein, from at least one measured or determined temperature of the refrigerant (K) in the refrigerant circuit and/or at least one measured or determined pressure of the refrigerant (K) in the refrigerant circuit , a control actual value characterizing the superheated state of the refrigerant (K) before or after the at least one compressor is determined and the control actual value is adjusted to a predefined or predefinable control target value by controlling the target heat source temperature difference (SW). <EOS>