I have to agree with the above post...sounds as if the fan(s) are not coming on. This may be a simple sensor problem, rather then the computer. I had a similar problem in a VW. You may want to ask an MB dealer to take a look at it, they may be familiar with the problem. I had to take a Pontiac to a Buick dealer (Buick engine and transmission) in order to get a tranny problem fixed.

I was in traffic today on the Interstate, 103 degrees, a/c on, and no hint of overheating. The needle was just barely above the center line and remained steady.

Good luck, I know it is frustrating.

John