Motor vehicle heating and air conditioning system with combined air mixing and distributing damper door

A heating/air-conditioning unit (1) has a heating element (3), first (9) and second (25) air flaps and several air channels (19,21,23) downstream from the heating element that are fed with a first air current guided over the heating element and a second air current guided past on the heating element. The first air flap fits in front of the air channels in a direction of flow.