Ok my car only blows on the floor vents.I have replaced the check valve under the hood and checked the vacuum lines with the pump and they are all ok.HOWEVER after about 5 minutes of driving it begins to blow normally!!What the hell could be causing this!And when it is blowing normally if i turn it off then back on it starts blowing only on the floors again.Please any help would be great...about to replace the hvac control panel since i have an extra one but would like some input before taking that trim off and probally craking the dash lol..Oh also it probally has nothing to do with it but the a/c **** is barely lit up at night

Mike
Mikekatie0425143@aol.com

 

Could be a sticky actuator door, or something got dropped down your defroster vent. Could also be a problem with the vacuum lines behind the HVAC controller or the controller itself.

I haven't gotten too deep into F-body HVAC but these are some things to check based on other cars I've looked at.

 

I'd say you still have a vacuum leak somewhere.

 

Could it possibly be the vacuum canister under the battery tray.

 

i would change out those dash controls. your getting vacuum to them because the doors are shifting, but they return to default when no vacuum is present, which is normal, but they should immediately return when the engine is turned on.