Re: Air condition stuck in defrost?
There is an access cover in the center of the top of the dash. There are several vacuum lines under this cover. There is also a vacuum connection behind the AC/heater selector switch at the dash, and other vacuum connections up under the passenger side of the dash/foot area.
There is also a vacuum line that routes to the rear driver corner that also is accessible behind the lower plastic trim on the driver door pillar, aft of the seat belt. These vacuum lines were pre-plumbed by Ford for future rear AC.
If there has been any work done in any of these areas, I'd start there.
I hope this helps!