A refrigerant circuit, comprising at least one refrigerant compressor, which compresses refrigerant fed at a suction connection to high pressure such that a compressor mass flow of the refrigerant compressed to high pressure exits at a pressure connection, at least one heat-emitting heat exchanger on the high-pressure side, having an inlet to which the refrigerant circuit feeds the compressor mass flow and having an outlet from which a cooled total mass flow of refrigerant exits, at least one expansion unit, comprising an expansion compression unit, which has an expander stage and a compressor stage and which expands an expansion mass flow of the total mass flow, conducted by the refrigerant circuit in the direction of the suction connection of the refrigerant compressor, starting from high pressure to an expansion pressure, and at least one cooling stage having at least one heat-absorbing heat exchanger to which the refrigerant circuit feeds a main mass flow comprised by the expansion mass flow expanded by the expansion unit, and feeds this main mass flow, after leaving the cooling stage, to the suction connection of the refrigerant compressor, characterised in that the expansion unit has a supercooling unit for supercooling at least the expansion mass flow of the refrigerant fed to the expansion unit, in that the expansion unit has the expansion compression unit comprising the expander stage and the compressor stage, and a branch, which branches off a supercooling mass flow from the total mass flow fed to the expansion unit and is connected to a feed conduit, which conducts the supercooling mass flow to an inlet of the supercooling unit, in that the expansion unit has an expansion member (122, 124) which is provided in the feed conduit and which expands the supercooling mass flow to a supercooling pressure, and in that the expansion unit has a connection conduit, which feeds the supercooling mass flow exiting from the supercooling unit to the compressor stage, which in turn compresses the supercooling mass flow to a return high pressure, which corresponds to least one high pressure of the compressor mass flow, to which the supercooling mass flow is fed, and in that the expansion unit has a mass flow return (240, 240') for the compressor stage, with which there is controllable a mass flow from a conduit leading away from the compressor outlet to a conduit (126, 102, 128) leading to the compressor inlet. at least one heat-emitting heat exchanger on the high-pressure side, having an inlet to which the refrigerant circuit feeds the compressor mass flow and having an outlet from which a cooled total mass flow of refrigerant exits, at least one expansion unit, comprising an expansion compression unit, which has an expander stage and a compressor stage and which expands an expansion mass flow of the total mass flow, conducted by the refrigerant circuit in the direction of the suction connection of the refrigerant compressor, starting from high pressure to an expansion pressure, and at least one cooling stage having at least one heat-absorbing heat exchanger to which the refrigerant circuit feeds a main mass flow comprised by the expansion mass flow expanded by the expansion unit, and feeds this main mass flow, after leaving the cooling stage, to the suction connection of the refrigerant compressor, characterised in that the expansion unit has a supercooling unit for supercooling at least the expansion mass flow of the refrigerant fed to the expansion unit, in that the expansion unit has the expansion compression unit comprising the expander stage and the compressor stage, and a branch, which branches off a supercooling mass flow from the total mass flow fed to the expansion unit and is connected to a feed conduit, which conducts the supercooling mass flow to an inlet of the supercooling unit, in that the expansion unit has an expansion member (122, 124) which is provided in the feed conduit and which expands the supercooling mass flow to a supercooling pressure, and in that the expansion unit has a connection conduit, which feeds the supercooling mass flow exiting from the supercooling unit to the compressor stage, which in turn compresses the supercooling mass flow to a return high pressure, which corresponds to least one high pressure of the compressor mass flow, to which the supercooling mass flow is fed, and in that the expansion unit has a mass flow return (240, 240') for the compressor stage, with which there is controllable a mass flow from a conduit leading away from the compressor outlet to a conduit (126, 102, 128) leading to the compressor inlet.