2003 s-10 4.3

 

You didn't give much information. Usually it is the mode actuator or the mode door.

 

I posted the same issues with my 03 Blazer, a few posts down from yours. All I get is hot or cold air through the dash board vents. Nothing at my feet or at the defrosters. As soon as the weather warms up a bit (going to be single digits in my area for a while) I'm going to start removing some of the hatch ways to see if the doors might be stuck.
If you come up with a solution, please post it.
Thanks

 

I found an old vaccum hose on drivers side of valve cover, 7/32 i.d. about 18 in. long that fed into tube going into cabin by the frame below brake booster, 4.3 automatic xtreme , has been leaking for sometime [MY BAD] everything works now & MPG's are back to 20-22 city 23-24 freeway ,the way it was .

 

Thanks! I'll take a look for that hose.
I have also been told that my lose of 4 wheel drive could have something to do with vacuum hoses.