A method for operating 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 pressure mass flow expanded by the expansion unit, and which is fed by the refrigerant circuit after leaving the cooling stage to the suction connection of the refrigerant compressor, wherein an emergency operation unit is arranged in the refrigerant circuit and comprises a bypass conduit bypassing the expansion compression unit with which is functionally associated at least one expansion element (232, 122), characterised in that the emergency operation unit is configured such that it detects an expansion disruption of the expansion compression unit, in that the emergency operation unit has a controller which transfers the emergency operation unit from the inactive state into the active state, and in that the emergency operation unit is configured so that, in the event of a disruption, in particular an expansion disruption, it transfers the expansion compression unit from an inactive state into an active state, in which said expansion compression unit, by expansion of the refrigerant placed under high pressure by means of the expansion element (232, 122), generates an emergency expansion mass flow (NEPM) for operating the cooling stage, said emergency expansion mass flow being fed by the bypass conduit to the refrigerant circuit for forwarding to the cooling stage. 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 pressure mass flow expanded by the expansion unit, and which is fed by the refrigerant circuit after leaving the cooling stage to the suction connection of the refrigerant compressor, wherein an emergency operation unit is arranged in the refrigerant circuit and comprises a bypass conduit bypassing the expansion compression unit with which is functionally associated at least one expansion element (232, 122), characterised in that the emergency operation unit is configured such that it detects an expansion disruption of the expansion compression unit, in that the emergency operation unit has a controller which transfers the emergency operation unit from the inactive state into the active state, and in that the emergency operation unit is configured so that, in the event of a disruption, in particular an expansion disruption, it transfers the expansion compression unit from an inactive state into an active state, in which said expansion compression unit, by expansion of the refrigerant placed under high pressure by means of the expansion element (232, 122), generates an emergency expansion mass flow (NEPM) for operating the cooling stage, said emergency expansion mass flow being fed by the bypass conduit to the refrigerant circuit for forwarding to the cooling stage.