Buick 89 air vent control

All I get when I select is air from the floor and def vents. How do I trouble shoot?

If you could find a diagnostic tree in a service manual for no air conditioning, it may help. I feel for you, I wouldn't want to have to go through these hot summer months with no air. Good luck!

Look under your hood on the firewall next to the brake booster you will see a little black box that is your vaccum tank. Look at the base of the tank you should have 2 vaccum lines going into it. One is from your engine the other goes inside. Usually the tank will have one line off causing your vents to default to the floor and defrost position.

I was in the dash today and pulled out as far as I could the panel which controls the vents. They are operated electrical.
But you were right on what it could be and thanks for your help, but these controls have wires going to them.