2002 f250 diesel ac only blows out defroster vents. heat only comes out defroster vent. where should i look. thanks joe

 

I've got an old 90 F250 4WD and I had to replace the vacuum assit on the brakes. They asked me whether it was over 4000 GVW or not. I didn't know so I guessed no and what I got wastoo small. It worked but what happened was exactly what you describe. The dampers under the dash are vacuum assisted and the only thing that worked was defrost. I bet you are loosing vacuum and the default setting is defrost.

 

found the problem. everyone thanks for all the help. i went to the local ford dealer and spoke to a mechanic. i have a 4x4 diesel with locking hubs and shift on the fly. i checked the vac lines from the vac pump they go to the vac reservoir ok then i isolated the the reservoir it held vac. 15" vac leaves the tank goes to breaks ,vent doors and a electrical switch on fender well that operates the locking hubs. that was the problem. new switch $59.