fig2 in each case partial streams are generated therefore a small volumetric flow of warm air is passed via the bypass passage 30 to the defrosting passage 21 although the latter is still at an elevated temperature compared to the air which otherwise flows through it but not to the same extent as with free flow through the bypass passage as a result warmed air is supplied in the region of the window associated with the defrosting passage 21 but this warmed air does not unnecessarily disrupt the temperature stratification in the vehicle the degree of heating is influenced by the extent of the desired temperature change which determines the position of the switching flap 34 fig4 shows a perspective illustration of a flap element which combines mixing flap 33 and switching flap 34 in this case the mixing flap segment 33 is curved convexly while the switching flap segment 34 is curved concavely the elliptical lens between switching flap segment 34 and mixing flap segment 33 forms a wall 31 which is also responsible for the fluidic separation between the bypass passage 30 and the first flow passage 15 in this region in which the slot 31 in the bypass passage 30 is also present this wall may also be part of a pivot arm 36 which widens radially outward in the embodiment illustrated however the pivot arms 36 are designed as webs formed separately fig4 shows two laterally arranged bypass passages 31 which each have.