A method of controlling a fan of a vapor compression system is disclosed. The vapor compression system includes a compressor, a heat rejecting heat exchanger, e.g. in the form of a gas cooler or a condenser, an expansion device and an evaporator arranged in a refrigerant circuit. The fan is arranged to provide a secondary fluid flow across the heat rejecting heat exchanger, e.g. in the form of an air flow. The method allows the electrical energy consumption of the fan to be reduced without risking instability of the vapor compression system.