1997 Chevy Lumina Mode selector switch don't change modes

Hello,
Just recently the a/c mode switch (Max, def, ac and recirculate) doesn't seem to select the different settings. I don't know if this selector is vacuam operated or electric. I got a parts pic from the chevy dealer but it don't show a lot. No where can I find anything about this in any of the manuals I have. Heck I can't even find the vacuam canister that is under the hood. Must get my eyes checked maybe. Can you give me any ideas as to where to start to check for the problem? If you would please email me at JrBluz2@aol. Com just in case I can't get back to this site to check your response. Thank you for your help.