I've got a 99 F250 and the ****ing heat won't work. the blower is good, the heater core is hot, but it won't blow out hot air only cold. i went and bought a new temperature control unit, it worked for a few days then stoped. the ALL of the fuses in and out of the truck are good. any suggestions.
You might want to try and check if something fell down the defrost vents and is blocking the blend door. I've seen this happen many times and have recovered pens, small wrenches, hairclips, etc... that were blocking the blend door. Do your usually have a bunch of stuff riding around on your dash? If you do, this might be your problem.
does it blow out in your front vents or just the defrost? It may be a vaccum issue? I may be completely wrong about with the heater, but mine it looks like everything is controlled off of a vacuum which is also shared with the auto locking hubs unit. hope this helps
1999 Black F350 4x4 Duelly
All stock, not for long!!!!