Air flow mixing device especially used in an air-conditioning and/or heating apparatus for automotive vehicles

The mixer, designed to distribute a main air flow (8) in variable proportions between hot (14) and cold (18) air ducts, comprises an open-work panel (40) in the hot air duct with apertures controlled by a shutter plate (44), and a rotary flap valve (50) in the cold air duct. The shutter plate and flap valve are connected by a control mechanism (54) that synchronises their operation, closing one as the other is opened.