Heating/cooling circuit for an air conditioning of a motor vehicle, air conditioning and its control method

The heating/cooling circuit has an evaporator (14) for cooling the air fed to the automobile passenger space, a heat exchanger (16) for heating the air fed to the passenger space and an external heat exchanger (22), associated with a compressor (24) for supplying a cold transfer medium. The pressure of the cold transfer medium in the external heat exchanger is adjusted between a maximum and minimum system pressure via expansion valves (28,30) associated with the evaporator and the external heat exchanger. Also included are Independent claims for the following: (a) an automobile air-conditioning unit; (b) a regulation method for an automobile air-conditioning unit