1996 E320. Air conditioned air is blowing warm on the driver's side outlets. Passenger side is OK. If car is sitting in shade or cool place when parked the a/c works fine for a few minutes and then reverts to the problem of warm on driver side and cool on passenger side. If car is parked in hot sun there is no cooling on the driver side, even momentarily. I've been told correction will require replacement of the a/c main control unit in the dash. Big bucks. Any help will be appreciated.