A method for the control and feedback control of the overheating temperature (T Ü) of a refrigerant in an evaporating means in the circuit of a plant system of a heat pump or cooling system, comprising the steps of: determining a virtual heat output of the evaporating means by forming a virtual energy flow balance; determining the target value (T Ü, Soll) for the overheating temperature as controlled variable in consideration of a virtual MSS curve, which corresponds to a borderline between a stable operating mode of the evaporation process and an unstable operation of the evaporator; and operating an expansion valve of the plant system, so that the overheating temperature (T Ü) is brought as closely as possible to the target value for the overheating temperature (T Ü, Soll), wherein the virtual heat output ( Q̇ Wv) of the evaporating means is formed of the functional dependency of the known variables, overheating temperature (T Ü), specific heat capacity (c" p (p v)) as well as specific enthalpy of the refrigerant in the saturated steam state (h"(p v)), the stroke of the expansion valve (y EXV) and a correction factor (K EXV) which is to be formed for every operating point and which expresses the heat output of the refrigerant for the valve stroke in the nominal operating point of the expansion valve, wherein the virtual MSS curve ( Q̇ Wv (T Ü,MSS)) is the function of the virtual heat output ( Q̇ Wv) over the overheating temperature (T Ü), and wherein the determination of the target value (T Ü,Soll,i) is carried out over the working range of the heat pump or the cooling system at the stability limit of the control system, respectively, said limit being determined by means of the rise angle (α TnV) in the temporal dependence of the temperature at the evaporator exit (T nV) and the distance of the overheating temperature (T Ü,I) from the limit value (T Ü,MSS,i) determined by the virtual MSS curve at each operating point (i) of the working range of the heat pump or cooling system, index i marking the current operating point (i) as the position of the current virtual heat output of the evaporating means ( Q̇ Wv,i) in the area of the virtual heat output from 0 to the maximum virtual heat output ( Q̇ Wv,EXV,max) limited by the design of the expansion valve. determining a virtual heat output of the evaporating means by forming a virtual energy flow balance; determining the target value (T Ü, Soll) for the overheating temperature as controlled variable in consideration of a virtual MSS curve, which corresponds to a borderline between a stable operating mode of the evaporation process and an unstable operation of the evaporator; and operating an expansion valve of the plant system, so that the overheating temperature (T Ü) is brought as closely as possible to the target value for the overheating temperature (T Ü, Soll), wherein the virtual heat output ( Q̇ Wv) of the evaporating means is formed of the functional dependency of the known variables, overheating temperature (T Ü), specific heat capacity (c" p (p v)) as well as specific enthalpy of the refrigerant in the saturated steam state (h"(p v)), the stroke of the expansion valve (y EXV) and a correction factor (K EXV) which is to be formed for every operating point and which expresses the heat output of the refrigerant for the valve stroke in the nominal operating point of the expansion valve, wherein the virtual MSS curve ( Q̇ Wv (T Ü,MSS)) is the function of the virtual heat output ( Q̇ Wv) over the overheating temperature (T Ü), and wherein the determination of the target value (T Ü,Soll,i) is carried out over the working range of the heat pump or the cooling system at the stability limit of the control system, respectively, said limit being determined by means of the rise angle (α TnV) in the temporal dependence of the temperature at the evaporator exit (T nV) and the distance of the overheating temperature (T Ü,I) from the limit value (T Ü,MSS,i) determined by the virtual MSS curve at each operating point (i) of the working range of the heat pump or cooling system, index i marking the current operating point (i) as the position of the current virtual heat output of the evaporating means ( Q̇ Wv,i) in the area of the virtual heat output from 0 to the maximum virtual heat output ( Q̇ Wv,EXV,max) limited by the design of the expansion valve.