I'm new to this forum, but found it extremely helpful! I found this site in desperation when my Ford dealer told me it would cost upwards of $800 to $1000 to diagnose and fix my heater problem, which was this: the temperature control **** rotated from hot to cold, but the air temp from the heater did not change. I found several forum users with the same problem, some describing the horrors of removing the dash to replace a broken blend door and/or actuato, which I assumed was the source of my problem. But there were also several suggestions to check the **** first (which tends to break easily, I guess). When I took the **** off, it was not broken, but what I noticed was that while it rotated easily, it did not turn the controller shaft it was attached to! For some reason the flat spot on the **** was not grabbing the flat spot on the shaft with sufficient force to turn the shaft. My fix was cheap and simple: I added a shim (made from a shaved-down wooden match stick) to the **** flat spot, and replaced the ****. So far, it seems to have worked! So the message to those with a similar problem is: check the easy things first. Make sure the **** is actually turning the shaft.

 

I just got my heater fixed too. On my 98 f-150 the blend door motor was bad, it wouldn't move at all.
One day i was just driving and the heater started blowing cold, then it was stuck on cold for rest of the day, then the next day it had switched back to heat and was stuck on heat until today. I had to fix it for the AC to work.

First i checked for a cracked ****, but it was fine, then i pulled out the control, that the **** is attached too, and i test it with a ohm meter, it worked fine too. So then i just assumed the motor was bad, cuz i couldn't hear or see it move. So i pulled the motor out and sure enough, it wouldn't move.
So i went to the ford dealer and they had a new one for me to plug in and make sure the motor was really the problem.

The new motor worked perfect, only $82 can with tax.

I was happy it wasn't the blend door broke.

Changing the motor wasn't too bad, just pull off that black plastic trim on the tranny hump, then undo the passenger side heater duct screw, and remove the 3 screws on the motor and wiggle the motor straight down , then wiggle it out, it's a pretty tight squeeze.

 

Seems like many of us need help when it comes to the AC or Heater. Maybe someone can help me? When I turn my AC on, it will blow nice cold air. When I accelerate, it seems the blend door closes and then will produce HOT air. No good. I have a 99 F-150. Is this problem related to the blend door or is it a vaccuum problem? Thanks for helping.