AC blowing warm/hot air from the upmost left and right side

[Versace]

Hello A8 Community

I have a problem that was making me mad on my previous A8 4.2 40V and the same goes for my newer S8 FL now. AC working well, but when outside temperature is between 17 and 22 and the AC setting to AUTO - 22* Celsius, I get warm air from the LEFT/RIGHT vents. If I turn the temperature down to LOW or 16-17 (depends on the outside temperature) I get cold air also from the sides.
When I tried to service this on my ex. 4.2, I changed the heater matrixes, refilled the AC gas and lubricant, cleaned and tested the heater control valves in the engine bay under the windsheeld - by the cabin air filter... Without success. But when the outside temperature is 30 or more degrees, it is okay, it blows cool air also from the L/R vents. When I change the air distribution to windshield/footwell everything is fine, the air coming out is in accordance with the AC setting.

What could that possibly be?