Update on dead ventilation control
I thought I would share my experience in troubleshooting the ventilation control on my 96 Blazer.
Turning the ventilation control knob was no longer changing the direction of air flow. It was stuck in de-fog mode.
I received a tip from a member of this group that it might be a vaccum problem. He suggested that I check the vac lines connected behind the knob....but before you rip out the dash (like I did), check the vaccum filter. It's a small T-connection in the vac-line (back-right corner near the black ball attached to the hood). The T-connection has a filter element...probably for water or oil. It is clogged. I have a strong vac before (engine side) but hardly any on the other side....which means that there is not enough pressure to activate the dampers. I bypassed the connection and all worked great. I will pick-up a new connection on the way home.
Hopes this helps another lost soul,