Why does my 1998 s-10 2.2 can turn the heat control knob to cool but still blows out hot air the switch is good?

Check your vacuum lines, this is what opens and closes the ducts. I had the same problem with mine. I just got it fixed a few days ago. The problem with mine was the compressor was leaking. Also i had the lines replaced, because they were sucked pretty much flat. To fix mine it was about $700. Wish i would have known that before I got it fixed.