Heat diagnosis.

Paste this into Google:

"ford explorer" "blend door"

You'll find lots of info on the various problems, and how to fix them. Basically, you remove the glovebox to access that area.

-Paul

There is also some more blend door info here that google probably can't find:

I think it's the second post.

Ulysses is pointing you in the right direction if you are having blend door trouble. Go to the Ford truck forum

and find the"free blend door fix" postings for "Jfrank" and "talon dad" and youwill find detailed instruction for determining if you have thatproblem. If you do then find their photo gallery postings (you willneed to register and spend a bit of time poking around) and you willhave detailed instructions with pictures for how to effect a repair.The alternative is to spend 100+ for a new plenum and a weekend tearingyour truck apart to replace it; or paying a shop 500+ to do the job.Having had this problem myself, I must say this is one of the biggestfiascos I have encountered in my 40 years of experience owning andmaintaining vehicles. It's just plain poor design on the belnd doorand absolutely no maintainability engineering done to ensure areasonable repair process iin the case of failure.