I searched through some old thread to try to find an answer but I might have missed somthing. I have a 2001 screw. Ac compressor is a little loud but it blows ice cold but when I give it a certain amount of throttle the blend door flips or somthjng and I hear the air rushing behind the dash. Any certain vacuum lines I should look for? I feel like when the engine draws or stops drawing x amount of vacuum it changes the doors position or somthjng. Any help would be very appreciated. Thanks on advance for any possible replies

 

You have a vacuum leak. Default position when vacuum is lost if defrost.

Check these common failure locations:

• There's a small vacuum tube that goes around the back side of your battery, these have been known to develop a leak.
• Also a small tube that goes through the firewall by the battery.
• Also check all the vacuum connections at the PCV valve.

Good luck....

 

There's also an accumulator back behind the battery that the tubes connect to.

 

Isn't the blend door motor actuated like this video shows.

 

Here's another video of a 2004 Expedition that has a vacuum controlled door

 

I had a similar problem in an 03 SuperCrew 4x2. It turned out to be a cracked T fitting on the passenger side firewall. The third port on the T fitting was simply capped off anyway, so I removed it and straight piped it. I think that third port is there to run the vacuum shift motor on 4x4 models, I think it's where the solenoid gets its vacuum supply from. My truck, of course, doesn't have that so it was factory capped.

 

when I was having problems with my vacuum leaks on a 1996 fi50 4.9 , I tied the blend door actuator open with a zip tie so the AC worked through the summer while i troubleshot and fixed the leaks I also installed an aftermarket round ball vacuum reservoir going to the HVAC I don't know if your vac controller is in the open like the 96 is, but might help you temporarily,