2000 Lumina ...can't get air to flow from any vent or floor, only out windshield defroster. Can turn selector knob to all ....MaxA/C, dash vent, floor vent, but air only comes out from defroster. Can selector be bad?

The resistor pack of the selector or the relay(under dash) could be faulty. I think the Haynes manual tells how to diagnose and fix it.