My 2000 S-10 Blazer heats up fine,,,,but no matter what setting I turn my **** to....the hot air comes out the vents as well as the floor and the defrosters, it switches to floor or defrosters fine,,,,but it always has heat blowing out the vents as well.....is there a door under the dash that is not functioning properly....I can't hear any vac. leaks when I turn the switch..
Any input is greatly appreciated!!

 

Sounds like there's an actuator that is not working, binding, or does not have vacuum to it. This chart is for manual HVAC, not automatic climate control, and will help you with diagnosis: