I have a 2000 S10 with 133k on a 4.3L v6. Today after being on the road for maybe 3 hours in 35 degree weather the air from the defraust stopped coming from the vents. you could hear the fan chruning but no air. I turned the selector to the AC setting and I got air out the dash vents. We stopped for about 2 hours to shop and when we turned it back on presto, everything was fine again. Where do I start looking for this issue?

-sp

Certainly someone has had this issue?

-sp
combining consecutive posts, sometimes it takes time to get an answer.

 

Certainly someone has had this issue?

-sp

 

You may have a vacuum leak at the climate control unit in the dash. You might have to remove the unit in order to check for a loose vacuum hose connection.
Sometimes if the leak is big enough, you can actually hear it in the dash.

 

or oyur thermostat is sticking
I just replaced my thermostat because it was sticking. Similar issue.
Next time watch your temp gauge, when does it open?

 

Temp guage was normal. In fact if I turned on the AC and set it to hot it was really warm.

-sp