An air conditioning system for motor-vehicles includes a thermally controlled expansion valve unit for regulating the expansion of the fluid upstream of the evaporator, depending upon the temperature downstream of the evaporator. An intermediate heat exchanger provides a heat exchange between the conduit upstream of the evaporator and the conduit downstream of the evaporator. The expansion valve unit is arranged in such a way that its temperature sensor detects a temperature of the fluid along the conduit downstream of the evaporator at a portion of this conduit which is located downstream also with respect to the intermediate heat exchanger. A connecting flange is interposed between the evaporator and the thermally controlled expansion valve unit.