The AC on my car constantly changes between blowing hard and slow. The middle vents don't blow air at all. The air that comes out is quite cold. My local mechanic charged $350 to change a vacuum control module. That had no effect.
Any ideas what is wrong?

Well if it had no effect why did you do it. You might ask your tech that. What you need to ask after he tells you that it needed it, is what is wrong with the thing now, and tell him to fix the problem this time. The one that concerns you not the broken part he finds as he plays with it. When its fixed he can tell you about all the things like your vacuum element that were broken but aren't part of your concern. Then once you know what it cost to fix it you can decide on the things with less apparant symptoms you wish to fix.

There is a good chance there was more than one vacuum problem and the rest may be simple. You are better off letting the tech that worked on it finish as he has already tested many things. Atleast I hope he has.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Thanks for the reply.