A method for controlling a vapour compression system , the vapour compression system comprising a compressor unit , a heat rejecting heat exchanger , an ejector comprising a primary inlet , a secondary inlet and an outlet, a receiver , at least one expansion device and at least one evaporator , arranged in a refrigerant path, the method comprising the steps of: - obtaining a temperature of refrigerant leaving the heat rejecting heat exchanger , characterized in that the method further comprises the steps of: - deriving a reference pressure value of refrigerant leaving the heat rejecting heat exchanger , based on the obtained temperature of refrigerant leaving the heat rejecting heat exchanger , - obtaining a pressure difference between a pressure prevailing in the receiver and a pressure of refrigerant leaving the evaporator , - comparing the pressure difference to a predefined first lower threshold value, - in the case that the pressure difference is higher than the first lower threshold value, controlling the vapour compression system on the basis of the derived reference pressure value, and in order to obtain a pressure of refrigerant leaving the heat rejecting heat exchanger which is equal to the derived reference pressure value, and - in the case that the pressure difference is lower than the first lower threshold value, selecting a fixed reference pressure value corresponding to a derived reference pressure value when the pressure difference is at a predefined level which is essentially equal to the first lower threshold value, and controlling the vapour compression system on the basis of the selected fixed reference pressure value, and in order to obtain a pressure of refrigerant leaving the heat rejecting heat exchanger which is equal to the selected fixed reference pressure value. - obtaining a temperature of refrigerant leaving the heat rejecting heat exchanger , - deriving a reference pressure value of refrigerant leaving the heat rejecting heat exchanger , based on the obtained temperature of refrigerant leaving the heat rejecting heat exchanger , - obtaining a pressure difference between a pressure prevailing in the receiver and a pressure of refrigerant leaving the evaporator , - comparing the pressure difference to a predefined first lower threshold value, - in the case that the pressure difference is higher than the first lower threshold value, controlling the vapour compression system on the basis of the derived reference pressure value, and in order to obtain a pressure of refrigerant leaving the heat rejecting heat exchanger which is equal to the derived reference pressure value, and - in the case that the pressure difference is lower than the first lower threshold value, selecting a fixed reference pressure value corresponding to a derived reference pressure value when the pressure difference is at a predefined level which is essentially equal to the first lower threshold value, and controlling the vapour compression system on the basis of the selected fixed reference pressure value, and in order to obtain a pressure of refrigerant leaving the heat rejecting heat exchanger which is equal to the selected fixed reference pressure value. <EOS>