Just recently the air flow when my a/c is on has directed itself to flow out of the defroster vents more than the vents in the middle of the dash of my '86 300SDL.

I had this problem with a '87 300D, and my mechanic (in another city now) made some repair or correction and didnt even charge me, he did have to go into the dash I believe or at least the upper console where the ATC unit and radio are held.

Any hints on what I might need to do or have done before I have any major work done?

Thanks,
Chris

sounds like the vacuum pods behind the dash need replacing. THis happened on my '86 300E except the air was not blowing out of the center vents. It was vacuum related.

Thanks, can you purchase them? are they difficult to replace?

Yes ! You can purchase at any MB dealers but
the problem is to find witch one or two vacuum elements is bad....there are seven to
eight vacuum elements you have to test them
first one by one and also could be the vacuum switch unit is bad.....to replace them
I will pay someone to do it ! Trust me.