2004 Mercedes-Benz S430 Question: the airconditioner and the rearview mirror

In the last couple of weeks, when I start the car, the airconditioner fan doesn't always come on. It sometimes comes on after driving for 5 or 10 minutes.
Another trouble that started about a month ago is that occasionally the rearview mirror will darken as if there were headlites behind me and this is in broad daylite.
Most of the time if I give the mirror a good tap with my hand it clears up the problem and then it occurs again when I get into the car at a latter time in the day or a day or two later.
HELP!