I was driving with the temperature controller off. All of a sudden I heard the blower turn and it got really warm in the van. I replaced the control unit with a used one and I have the same problem. What else can I try?

 

The problem may not be the control unit, Thats if you are talking about the center panel on the dash.The problem maybe the blower resistor, These can many problems. Under the dash behined the glove box.

 

Do you have automatic temperature control? What speed was the blower running at (high maybe, based on sound) when this incident happened?