My air has been finicky lately. At first, it would switch do defrost no matter what the selector was on while under throttle above 2k rpm. It did this more and more often until this morning, where it's only coming through the dash/defroster vents no matter what is selected, fan speed, or temp is set at. Heater core and blend door were replaced just after christmas. What's the problem?

Thanks!
- B

 

I'm not sure if it is the same deal, but that sounds like what was happening in my Camaro a couple years back... They ended up replacing the thermostat and the problem was gone.

IT was basically same problem, but when just cruising it would blow through vents, but if i would give it gas at all it would dye down and switch to dash/defrost.

 

Air started working when I started the truck earlier after being shut off for about 7 hours. Still doesn't put air out under throttle.

 

possible vacuum leak

 

I have the exact same thing, there's another thread on it https://www.f150online.com/forums/hv...ash-vents.html

mine works properly once it has warmed up