Automatic heat and Air Conditioning

hopefully this will give you a place to start... Usually with manual AC systems, when the blower motor only operates on the max setting, it is related to the blower motor resistor. The highest setting bypasses the resistor and that's why the motors only work on high. With your Auto-temp control I haven't been able to find if you have a resistor but there will be come kind of blower motor control (either a resistor or control module). Maybe a call to your local Ford parts department will help clear this up. I found a thread posting on the Ford diesel forums, maybe it will help you some http://www.powerstroke.org/forum/6-0l-electronics-discussion/29426-blower-control-module-part-number.html