I recently (3 months ago) purchased a '95 sl500 with 77k original miles (confirmed). Today, the a/c (blower?) started making strange noises-like a small chain saw! What could this be? Is it difficult to repair? Any thoughts would be GREATLY appreciated!

There is a strap that clamps over the blower motor holding it in place. This strap can break and sometimes the plastic housing that attaches it can break too. When either breaks it allows the motor to move around and the fan blades rub the housing making the noise you describe. To diagnose what has actually broken the covering over the blower has to be removed.