The air had been blowing cold from the vent...selection seemed to be working well. But, over a 3-week period, it worked intermittently and then stopped working...only getting air out of defrost. I'm guessing it's a vacuum issue...but not sure if it would be under the dash or in the engine bay...any suggestions or schematics?

 

I'd suspect under the hood first, due to all the heat and vibration.

My own truck had a cracked check valve in the black vacuum line at the reservoir beside the evaporator.

I've seen the white hose at the air recirculate flap motor get chewed off by rodents and cause this, too.

If you do look on the dash, look for vacuum lines that could have gotten caught under your passengers shoes. I've seen these hoses pulled down several times.

 

Look for the "Infamous" white vacuum line under the hood, passenger side that runs to the vacuum modulator that controls the blend door function. It becomes brittle and falls apart in sections. I've seen 4 trucks of our vintage with this problem and all 4 had to be repaired.

 

That's what numerous ones are...^^^^betting that's what it is.

 

Thanks, all...it was the vacuum line in the engine bay. Took 5 min and less than $10 at the local O'Reilly's to get it fixed. Appreciate all the inputs!

 

Glad you found it and replied back with the fix!

 

I have a '94 with no heat control... replaced core, fixed actuator that selects reg air to "max air".. but still no "hot air.. all the venting works correctly ... def, floor, mix.. I just get no hot air... pulling my hair out.. I am doing a mostly restore to this supercab XLT 2WD 5.0.. all interior out and repainted, putting vinyl flooring new headliner.. its all waiting for the silly hot air issue to be fixed.. yes I did a search but there arent any "how to " videos or photos for 92-96

 

The blend door is controlled by the cable behind the glove box. Is the door moving when you change the temperature setting?