I have a 1993 Dakota 4x4 LE v8 and the switch to the air vents is stuck on defrost vent. I changed out the blower control module/ resistor and no change. Does anyone know if this is vacuum controlled or electrical? Everything else is working just will not switch!

 

Yep, vacuum controlled, and you aren't getting vacuum to the control head. The plastic lines under the hood get brittle, and break, thus you lose vacuum, so, the vents default to defrost....... (as being able to see is more important than warm toes. )

 

Look for disconnected/broken or kinked vacuum supply line to the control head.
I just fixed mine the other day...and my experience was it was the supply line was kinked totally.

 

Where do I find these vacuum lines? Are they under the hood or is it in the cab? I've been searching but can't seem to find any graph with the vacuum lines or control head location.

 

Should be a sticker under the hood for vacuum routing..... don't know if it includes the HVAC stuff though. The lines you are looking for are indeed under the hood. Likely just one broken line, that supplies vacuum to the HVAC controls.

 

If it's the same as my 87 the vacuum line you want goes through right under the heater core hoses on the firewall and goes to a vacuum manifold above the brake booster.

It was broken on mine.

 

The VECI under the hood shows the under hood portion; the factory service manual will have the in-cab portion. FSM will also have the VECI (Vacuum Emissions Control Information) in it.

USUALLY it's the under-hood portion broken.

RwP