Heating and/or air-conditioning apparatus, particularly for a motor vehicle

A heating and air-conditioning apparatus for the cabin of a motor vehicle. The apparatus includes a chassis within which air flows and equipped with an air-blowing mechanism and heating and cooling units for cooling and heating the air and a member for controlling the heating unit. At least one airflow duct communicates with the chassis, and at least one mixing shutter, with a variable degree of openness, controls the air stream towards the duct. The mixing shutter is arranged in the overall direction of the air flow downstream of the heating member and transmits additional air passing through the heating unit when the fresh air passage is wide open, and governs in an intermediate position of closure of the air flowing through the heating unit. The mixing shutter also switching a control member controlling the operation of the heating unit between an off and on position.