A motor vehicle air conditioning system including a Coanda effect air distributor device and mixing means which allow to vary the temperature of the air available to the different outlet conduits of the distributor device for the same setting of the means for regulating the temperature of the system. In this way, for a same setting of the temperature regulating means, the air conveyed to the outlets situated at the base of the windshield is at a higher temperature than the air conveyed to the other outlets and in particular to those adjacent to the floor of the motor vehicle passenger compartment. Preferably, a third, still lower temperature level is available to the outlets situated in the front part of the dashboard of the motor vehicle in the direction of the motor vehicle occupants.