I have a 1999 5.4 and lately when I get it gas the air quits blowing through the main vents and blows through the defroster vents. My neighbor's is having the same problem on his F150 - not sure of year - as well. I did replace my PCV valve and hose asssembly ( Check Engine Light has been on - lean both banks) as it did have a few holes in it which cleared my code but not the AC issue. I have been told it is vaccum related but can't find and more leak signs - Any help would be greatly appreciated.

TommyRox

 

Go to the HVAC section, you'll find several conversations on the first page that address this symptom.

 

projectSHO89 thanks for the reference - wow, this really seems to be a common problem...