Heater distribution switch not switching
My rotating switch that selects MAX A/C, A/C, DEFROST, FOOT HEAT, FACE HEAT, ETC. is not working all of a sudden. No problems generating hot air or air conditioned cold air, but almost everything I get comes out of the defroster ducts with very little coming from the selected ducts. I suspect the actual porting itself and not the switch since it will still turn everything off if I set it in the OFF position.
I've checked for open fuses in the box under the hood, and looked around under the hood near the heater assembly for disconnected wires or vacuum lines, and see nothing out of place. i'm not sure if the air distribution is mechanically actuated with cables, vacuum motors, or electrical actuators. The dashboard switch appears to be electric only.
30 years ago, I ran an automotive repair shop. Not so these days. Can this be diagnosed by some kind of code reader? If so, would I be better off going to the dealer or would a local reputable shop have the experience and equipment to diagnose and repair it?
Thanks in advance for any insight