GM / General Motors: Cadillac Eldorado Problem

Hi. A friend of mine used to own a 93 Cadillac Eldorado with the Northstar
engine. Shortly before he sold it, the vents in his car would no longer work,
i.e., vents open, no air coming out of any of them at any setting. I am
looking at a 1993 Cadillac Eldorado with Northstar engine, and while checking
things out noticed this car has the same problem
Anyone experienced this?? Any solution ideas/? How big of a job, I would
imagine this to fairly substantial amount of work.
Any and all help much appreciated.
Thanks in advance,
George D. S.