You did not mention if the air comes out of the vents where you direct it to go?
It may be that the diaphrams on the cells/modules that control the heat/cols aire mixture is shot. Or it could one of the modules behind the dash. On my 190 there are three behind the dash and one underneath the wiperblade motor. If these are not in proper working order, the outside/heat/cold air mixture is all mixed together and the air does not come out where you direct it to come out of on the climate control panel. Which could also be part of the problem or even the AC relay.