An automotive air conditioning system comprising: an air cooling circuit including a compressor, a condenser, an expansion valve and an evaporator; an air heating circuit, including a flow rate regulation solenoid valve arranged to regulate the flow rate of a heat transfer fluid through the heater; and an electronic control unit. The electronic control unit is configured to receive a measured evaporator air temperature and a set cabin air temperature and to switch the operating condition of the compressor when the measured evaporator air temperature is higher or lower than at least one on/off threshold temperature computed based on the set cabin air temperature.