i have a 07 f250 6.0L and my ac/heater defaulted to defrost only, ive checked vaccum lines and cant come up with anything, tried replacing the blend door thing and that didnt fix it...any ideas??

 

They usually do that when there is a vacuum leak and you engage 4 wheel drive. Does it do it when you're selecting 4x4 on the switch, or just anytime?

 

Get a hand pump and put vacuum on every line that connects to every component except for the tank itself. did you install the blend door actuator correctly? I used to screw them up all the time until i figured out how to get them in correctly.

 

Did you find the problem because when i turn my truck on i have the same problem but after five minutes or so then it starts blowing out the vent.

 

call berge ford in mesa az. and ask for richard freeman he is my uncle and he is a guru when it comes to any fords he is the master mechanic there

 

The 4 wheel drive thing is the orings on the hub or the seal on back is shot, most times I think it is the Oring though, my hub **** had a hole in it but a little silicone cured my problem..

 

I have two brand new hubs, o-rings, and wheel bearings, auto 4x4 still doesn't work. Also swapped pumps on the passenger side inner fender under the hood there, with a known working one, still doesn't work!

 

don't know then, follow each line from the tank and see if any are busted.

 

Had the same prob on 05. First off the rubber lines were rotted off the inner knuckle and thus auto 4x4 wouldnt work. Then the same vent issue, turned out the little vacum selenoid on passenger side behind battery was shot, it was stuck open and therefor wouldnt let the system build a vacum. It was like 50 bucks from ford now auto hubs work and everything is right.

 

That's my next step, just too lazy!