I have a 99 f350 diesel with 182000 miles. I can not get my heater to blow hot air. My a/c works fine and when I turn my heater on it blows but no hot air. I left the climate control in the red and was using the vent and was going up a long hill and all the sudden it started blowing hot air, so I turned it back to the blue since i didn't need the heat at the time. It has not worked but that one time. Could this be my climate control? I was told by a friend it could also be a blending door? not sure if that is the correct name for it or not. Any help would be great. thanks!

 

Sounds like the blend door actuator. It lives behind the glove box. I've replaced a few of these on other ford models but not on one like yours. Anyone else?

 

I currently have the same problem in my 2000 F350. It is the actuator that is flakey. I just have to tap on it to get it to work. Not really much of a problem being in Fla. but it does get cold in the mornings.