Clima behaves strange

Last winter was cold and long. One day I was driving with clima set at 25 celcius on inside and outside air was some 20 below zero. Something clicked in the heater and flaps started to work strangely. Now at warming up heat is OK, while driving gets cold in the feet area, weak blowing from medium grills at bi-lev and nothing at all at auto. Anybody got clue? Vacuum ducts are and fan are ok, servo - perfect!