When I turn the a/c on very cool air comes out of the passenger side vents (the one next to the door and the middle vent on that side) and warmer air on the drivers side. Any suggestions???

The best way is go to a air condition specialist and have him fix it. If you do not know anything about the subject and try to fix it and don't,the specialist has to work twice as hard to fix it. That will make the bill higher.

Try taking it to either a Mercedes dealer or a shop that specializes in heat and a/c.