a/c doesn't work on drivers side
 

I have a 96 e320 with the inline six and 140,000 miles. My a/c blows cold on the passenger side vents but not on the drivers side. When I turn on the recirculate button it will eventually get a little cooler. I believe one of the flappers in the duct is not working. Can anyone help with locating the right one and how to diagnose the problem. Are they vacuum operated?

No, it's low on refrigerant. Flaps don't control blending of heat/cold on the 210.

Just saw your post, but have to ask the Stupid question:

I'm have "heat" issues on my 1988 300 SE, w126, just had it serviced and inspected - is it possible low "refrigerant - are you talking coolant" could affect the heat? however my seat heaters work ... not blazing hot, but at least kept me from freezing my a$$ off!

TIA

I have the same car and I can tell you that you are low on r 134 refrigerant. This is a tell tale sign that it is low. Do you hear a hissing sound from the vents? Have it charged up and your problem will be solved. Having said that, these model cars notoriously have leaky evaporators so beware. I had to replace mine as I was adding refrigerant once a week!

Low refrigerant.