I couldn't find an appropriate forum for this, so I'll start it here and see what the master moderator does with it.

Two trucks, same issue. A 2006 F-150 screw and a 2002 F-350 Dually, Lariat. Both of them will have hot air blowing at idle when you first start. Even after a few minutes. It's cooler outside in the sun! When the RPMs go up on the F-150 the air starts blowing cold. When the RPMs go up on the F-350 it only starts blowing cold air if you are in motion. Sitting at a stop wont do it. Both trucks actuators and blend doors are working fine. Once we have cold air we can change to hot air and back to cold. I checked coolant, and according to the cheesy gauge it's fine. But there must be a reason behind this mystery and the worse part is it is with two different trucks. Was up wit dat?

 

Somebody mentioned something about this recently and they said to replace the fan clutch that seems to be the issue people are having. I can't remember right off the top of my head but maybe somebody will chime in to help me out here.