Just want to know where to look for solution. I am mechanic and lots of times the ac/heater control panel is the culprit. Have already tried that from the wrecking yard from a van that looked like it was maintained. Just was hit on the front and totaled it. It looks to me like the vents keep blowing in front when heater is turned on and not the floor. Not sure if blend door is inoperable, or if van has blocked heater core in front.

To get heat in the van you have to turn on the front for the rear to be turned on. I don't like this requirement myself because when I was using van for my carpooling the guys wanted a/c on and me and my buddy up front were freezing. I put the front on lowest fan and the rear on the highest with switch set to rear operator control. After about 10 to 15 minutes the rear would finally over power the front blowing cold air and van would get warm but no defroster on front windshield. Please help cause I am so busy with regular job and car repairs on my days off.