The air conditioning housing (2) forms an air channel whose first opening (16) blows air onto the inside of the windscreen and whose second opening (15) feeds air to the bottom of the passenger compartment. A distributor (12) divides the air channel into a first channel (14) importing outside air and channel (13) importing inside air, and uses first and second fans (6a,6b) to blow outside and inside air respectively at total pressure into the compartment. The first opening is opened and closed by a switch flap (19) rotating in housing and flap (18) similarly controls the other opening. The two flaps are so swivelled or rotated that both channels (13,14) are separated in air discharge with both opened (15,16) by the respective switch flaps. The two fans are adjusted to vary the volume of outside air through the channel (13) to increase this relative the total pressure of the first fan and thus exceed that of the inside air along channel (14) in relation to the second fan total pressure.
