Air cabin to demister control problem

[luv]

Hi guys,
I've recently bought a 4.6L V8 '02 Explorer for my wife as the main family car and to tow the caravan.
When I was towing the van last week up the freeway, in 35degree celsius weather. When I had to accelerate up a hill, it'd drop down a gear and the revs would go from 2,000 to 3,000rpm. Whenever this happened the air con would go from the cabin vents to the demister. Making it too hot in the car, especially for the kids in the back.
Does anyone know what this could be? I'm thinking some kind of vacuum leak in the controls, so extra rev's changes the air pressure in tubes/pipes.

Also, the fan always seem to blow a little on the feet. Is this normal?
Many thanks.

 

[luv]

Thanks for the overwhelming replies guys. lol
I'm new here and not familiar with these cars at all.
By looks of it, could it be the common plenum linkage arm failure thats creating my problems?

 

[ponkotsu]

Thanks for the overwhelming replies guys. lol
I'm new here and not familiar with these cars at all.
By looks of it, could it be the common plenum linkage arm failure thats creating my problems?

Test out the controls and see if the air goes where it should. I just did mine today, and it seems to be working fine now. It's a major job. Have to remove the dash and lay it on the front seat. You can probably pull out the radio and get a look in there and see if anything is broken. That's how I accidentally found the problem in my Aviator.