The invention relates to an air conditioning system for a motor vehicle, with at least two coolant circuits as well as a refrigerant circuit. The refrigerant circuit comprises a compressor for the compression of the refrigerant, a heat exchanger for the cooling and liquefying of the compressed refrigerant, an expansion device, and a heat exchanger for the evaporation of the two-phase refrigerant. The heat exchangers are designed as coolant-refrigerant heat exchangers in each case for the heat transfer between the refrigerant circuit and at least one of the coolant circuits. The refrigerant circuit is moreover constructed with a heat exchanger for the heat exchange between the refrigerant and an air mass flow to be supplied to the passenger compartment of the motor vehicle as well as with an element, arranged downstream of the heat exchanger in the flow direction of the refrigerant, for changing the throughflow cross section.