It has resistance, but doesn't seem as much. As far as I can tell, the knob only controls one cable that is working properly. The cable moves an arm on the bottom of the evaporator box. Is there a second cable or electric switch I should be looking for?

I'll look for the control valve and see if it's moving properly in the morning. I'm trying not to take the controls out because I would have to disassemble a big portion of the dashboard ... which will suck.