Air-conditioning system for a motor vehicle

An air conditioning system for a motor vehicle with an engine coolant circuit for heating and a refrigerant circuit for cooling an air stream to an interior compartment of the motor vehicle, said system including an air conditioning unit (3) with a heating coil (7) disposed in the engine coolant circuit for heating the air stream and a cooling coil (5) for cooling the air stream, the refrigerant circuit comprising a refrigerant compressor (12) and, in a first partial circuit a first heat exchanger (14) arranged downstream of the refrigerant compressor (12) for dissipating heat from the refrigerant compressed in the refrigerant compressor (12), an expansion device (16) arranged downstream of the first heat exchanger (14) and upstream of the cooling coil (5) by which the air stream through the air conditioning unit (3) is cooled, a refrigerant return line to the compressor (12), and a second partial circuit extending from the refrigerant compressor (12) to a refrigerant-engine coolant heat exchanger (27) disposed in the engine coolant circuit for transferring heat from the compressed refrigerant to the engine coolant and then to said expansion valve (16), the path from said expansion valve (16) back to said compressor being common to said partial circuits.