air condition/ heat control only works on highwhat is this problem please help.

What is your question?

# 1, in my van the control knob for the air condition and heat only works in the high position.all works well.but must be on high speed to work. # 2, also from the passenger side of the inside of the van under the dash blowing on the floor and anyones feet is cold air when the heat is on and heat when the ac is on.but never in the off possion.help please