Ford F-350 1999 Air Conditioner Blower Problem
A/C and heat work fine on high speed only-blower fan will not operate in any other positions.
Any help is appreciated?

 

Generally that means that your blower resistor is bad. At the lower speed settings the current for the blower motor goes through a resistor to decrease the current and voltage to the motor. If it goes bad you can only get high speed. I'm not familiar with where the blower resistor is located on your year vehicle. Hopefully someone else will be able to tell you.