My '94 Dakota just passed 250k.
The vent controls are stuck on defrost. I can push the different buttons but I can't hear any air noise when I try to change to floor vents etc. Temp cable is fine, air is still good and hot on these cold mornings. I'm asssuming this is a vaccum control for the vents. Any tricks to this? At least it's stuck on windsheild defrost. TIA

 

Either there is a problem with the doors themselves, or, a vacuum issue.

The design of the system is that, in the event of loss vacuum, it will default to defrost (windshield) position.
Check your vacuum lines coming off the engine, and than the nice bundle of them behind the heat/AC control unit in the cab.

 

Thanks for the reply. Does anyone know which side (Driver or passenger side) of the firewall the vaccum line passes through?

 

I don't know, I'll GUESS more towards the passenger side.
The vacuum lines are fairly easy to locate. The come straight off the intake manifold, both drivers and passenger side. Just follow the vacuum line for the brake booster back to the engine, this will show you the vacuum ports on the drivers side. Vacuum ports on the passenger side is on the exact same location.

 

Its pretty much in the middle. Small plastic hose.

 

Ok, found the cracked vacuum line and repaired - vents back to normal.

Found one other problem.
This is the 3.9 V-6. O the driver's side of the intake, just to the rear of the brake booster hose, there is a small vacuum solenoid (I think it's canister purge solenoid) with two 1/8" plastic lines, one goes to the EGR and the other I'm not sure. The solenoid has the two lines stacked one atop the other. Both of these are broken, (it's a 25 yr'old ride). Does the orientation matter?
'

 

You should have a vacuum diagram under the hood. That will tell you where they go. We also have the service manual that has the diagrams, it is in the FAQ in this section.