97 XJ air only comes out defroster

[superdave]

I have pulled the controls out and all 6 vac lines are connected. The one coming through the firewall is connected to the vac canister which is getting vac from the intake manifold. I can't imagine that it isn't getting enough pull from there. Any thoughts? Not that it should make any difference but this is a carb'd 350 not the 4.0.

 

[Alexia]

The plastic arm up that connects to the upper flap commonly breaks.

Here is a diagnosis video I made on the same HVAC unit to make sure all the functions worked after repairing the plastic arm.

 

[01yellowxj]

On my 99 I traced down all the vacuum lines off the intake manifold back to where they ended looking for a crack or break. Fond one hear the cruise control, it was a vacuum line going to a vacuum ball behind the bumper.

That allowed it to work but during hard acceleration it would swap back to defrost. I started looking for another vacuum leak and this time found it to be the one that goes through the fire wall and connects to the black vacuum in that group of lines going to the controls. I sliced into the black on behind the glove box, ran another vacuum through the firewall and connected it to the factory vacuum running over to the intake manifold. Capped off the other side of the splice and the one at the firewall and she works great!

 

[red94yj]

Mine was the vacuum canister connection by the passenger side of front bumper, well actually the vacuum canister is gone.

 

[old_man]

The most common cause of defrost only, as you may be able to tell from the few posts already, is a vacuum leak. There are tons of threads on tracking down vacuum leaks on here. Good Luck.