New to forum I have looked for info. I have a 2000 s10 blazer 4.3. Can someone tell me which actuator control's the adjustment for the control to the feet outlet. I have bottom of dash off and both actuators move but neither seem to change to feet. Need to know which one to replace.

 

If you can access each of them, you should be able to tell if one is working or not by supplying vacuum to the inlet and seeing if it moves. Sucking on it with you mouth might be sufficient.

Search the forum for vacuum hose schematics/diagrams and you should find a diagram to help you.