Refrigeration system for a vehicle comprising a refrigerant circuit having a dual flow heat exchanger, wherein - the dual flow heat exchanger can be operated as a refrigerant condenser or gas cooler for an AC mode or as an air heat pump evaporator for a heat pump mode, - a first flow (2.1) of the heat exchanger has a first refrigerant connection (2.10) and a second flow (2.2) of the heat exchanger has a second refrigerant connection (2.20), wherein for the dual flow through the heat exchanger in AC mode the first refrigerant connection (2.10) is a refrigerant inlet (E AC) and the second refrigerant connection (2.20) is a refrigerant outlet (A AC), - for single flow through the heat exchanger in heat pump mode the first and second refrigerant connections (2.20) are refrigerant inlets (E WP), and - the heat exchanger has at least one third refrigerant connection (2.30) which as a refrigerant outlet (A1 WP) in heat pump mode is fluidically connected to the first flow (2.1) on the refrigerant outlet side and to the second flow (2.2) on the refrigerant outlet side, characterised in that - for controlling the flow of the refrigerant from the second refrigerant connection (2.20) to the first refrigerant connection (2.10) a unidirectional valve element (2.4) fluidically connects the second refrigerant connection (2.20) to the first refrigerant connection (2.10), - the third refrigerant connection (2.30) is fluidically connected to a valve element (2.5) for controlling the refrigerant emerging from the heat exchanger, - the heat exchanger has a fourth refrigerant connection (2.31), which as a second refrigerant outlet (A2 WP) in heat pump mode in addition to the third refrigerant connection (2.30) is fluidically connected as the first refrigerant outlet (A1 WP) to the first flow (2.1) on the refrigerant outlet side and to the second flow (2.2) on the refrigerant outlet side, and - the third and fourth refrigerant connections (2.30, 2.31) are fluidically connected to the valve element (2.5) for controlling the refrigerant emerging from the heat exchanger. - the dual flow heat exchanger can be operated as a refrigerant condenser or gas cooler for an AC mode or as an air heat pump evaporator for a heat pump mode, - a first flow (2.1) of the heat exchanger has a first refrigerant connection (2.10) and a second flow (2.2) of the heat exchanger has a second refrigerant connection (2.20), wherein for the dual flow through the heat exchanger in AC mode the first refrigerant connection (2.10) is a refrigerant inlet (E AC) and the second refrigerant connection (2.20) is a refrigerant outlet (A AC), - for single flow through the heat exchanger in heat pump mode the first and second refrigerant connections (2.20) are refrigerant inlets (E WP), and - the heat exchanger has at least one third refrigerant connection (2.30) which as a refrigerant outlet (A1 WP) in heat pump mode is fluidically connected to the first flow (2.1) on the refrigerant outlet side and to the second flow (2.2) on the refrigerant outlet side, - for controlling the flow of the refrigerant from the second refrigerant connection (2.20) to the first refrigerant connection (2.10) a unidirectional valve element (2.4) fluidically connects the second refrigerant connection (2.20) to the first refrigerant connection (2.10), - the third refrigerant connection (2.30) is fluidically connected to a valve element (2.5) for controlling the refrigerant emerging from the heat exchanger, - the heat exchanger has a fourth refrigerant connection (2.31), which as a second refrigerant outlet (A2 WP) in heat pump mode in addition to the third refrigerant connection (2.30) is fluidically connected as the first refrigerant outlet (A1 WP) to the first flow (2.1) on the refrigerant outlet side and to the second flow (2.2) on the refrigerant outlet side, and - the third and fourth refrigerant connections (2.30, 2.31) are fluidically connected to the valve element (2.5) for controlling the refrigerant emerging from the heat exchanger.