2003 Chrysler Town and Country Heater Fan won't shut off/do

I have an automatic climate control heater/air that I can shut off the automatic part and control myself. I'm having issues with my heater fan. The fan only blows at high speed it won't turn down to low or med. This happens even when I turn the heater/air conditioner off. When I turn system off, the vents shut off where nothing comes out of the vents but then it sounds like it is pushing the air out by the front passenger floorboard area or somewhere under the dash. The heat seems to operate okay as far as temperture it heats up and cools down, vehicle temp runs pretty much in middle of temp gauge where it always does.