Once I get my 190E engine back together, I will be troubleshooting almost the same thing. I get very hot air out of the lower, window and side vents all the time. The center blows only cooler air. This is even with the A/C on. The heat control makes no difference.
I seem to get some kind of mix in the center vent. I can tell that there is a spot where cool air is and where hot air is.
Is my problem the same valve?
'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)