Electronic hvac controls not working
 

I've been searching a bit for the answer to this but I haven't found a clear answer. I have the digital dash in my 88 GTA and my vents are stuck on defrost. I have the HVAC system with the pushbutton controls. Is this control completely electronic or does it still use vacuum to open and close the diverter doors?

pic
 

Had a pic up, but it didn't post.

It should be vacuum operated. The defrost setting is it's default setting which is a good indicator of this.
Check for an unhooked, broken, or pinched hose leading from the backside of the controls going through the firewall just to right side of the transmission. Unfortunately, I do not know where it might connect to the engines' intake system.