Method for controlling an expansion device of a vapor compression system during start-up using rates of change of an evaporator inlet and outlet temperature

A method for controlling a vapour compression system during start-up, the vapour compression system comprising a compressor, a condenser, an expansion device having a variable opening degree, and an evaporator arranged along a refrigerant path, the method comprising the steps of:

• starting operation of the vapour compression system,
• monitoring a first temperature, T1, of refrigerant entering the evaporator,
• monitoring a second temperature, T2, of refrigerant leaving the evaporator,
• deriving a first rate of change, ΔT1, of the first temperature, and a second rate of change, ΔT2, of the second temperature,
• comparing the first rate of change, ΔT1, to the second rate of change, ΔT2,
• based on the comparing step, determining whether the evaporator is full or is not full, and
• controlling an opening degree of the expansion device according to a first control strategy if the evaporator is determined to be full or controlling the opening degree of the expansion device according to a second control strategy if the evaporator is determined to be not full.