Dual zone climate control, one side warmer
 

I have a '98 E300 and when I have the driver and passenger side temperature set the same, the driver's side blows considerably warmer than the passenger's. If it were reversed I would not be too concerned as my wife is usually cold (open to interpretation). I suspect a vacuum leak may be the cause, but no idea where to begin my search. Please help. Only noticeable when using a/c.

drivers side warmer,
 

i believe it is that the freon is low. the way you can check is drive the car, put the temp selector for both sides at full cold, make sure the ec button is on, this will turn off the compressor, if during this time the drivers is still warm you may have a vacuum element or control problem or possibly a duo heater valve binding open or not seating inside properly. if during this test you find that the temps are closer to the same now, what is happening is the froen is low and it is not allwoing proper circulation of freon to the drivers side, not allowing for proper cooling, i have also seen a partially clogged receiver dryer cause similar problems. please let me know what you find. Ray

You were right on the freon low diagnosis. One can in and I'm back to normal. Thanks.