Welcome to the BBS Elizabeth!
Does any of your other vent control work? ie. defrost, defrost heat, heat, bi-level, vent, etc?
If not, chances are good that the control unit solder joints are cracked and don't allow proper control of the mode selector. I've got a sticky thread in this forum on this issue.
http://www.bbs.legacycentral.org/viewto ... =10&t=1142
Depending on your skill level, you could replace the HVAC control unit with another one, or try and have the joints soldered.
What year is your Legacy?