The present invention relates to a cooling system of a refrigerator, particularly of a refrigerator including a refrigeration compartment and a freezer comprising a compressor attached to at least one condenser by a segment of a refrigerant tube, wherein a first refrigerant line leaves from the condenser and returns to the compressor, and a second refrigerant line leaves from the condenser and returns to the compressor. In the preferred embodiment of the present invention, the compressor has at least two suction inlets, wherein the first refrigerant line is connected to the first inlet and the second refrigerant line is connected to the second inlet, and both inlets have each a suction valve. In the optional embodiment of the present invention, the fluid compressor comprises at least one fluid selection device directly connected to the at least one suction inlet, and the fluid selection device receives at least two supply lines, and is able to selectively switch pressurized fluid from one of them, to the suction inlet of the fluid compressor.