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.

First see if it has enough refrigerant. Usually that's the problem.

is their only 1 main line for freon to go into ??
since its separate climate control

That is just amazing to me, but I've read it so many times there must be something to it.

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2012 E350
2006 Callaway SC560

It's a vacuum problem, the flaps that close the path from the heater core to the evaporator are not working. The side vents are on a separate system from the center vents. The problem most likely is a vacuum leak in a line or the climate control panel ( the buttons).
knutz

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'90 190e 2.6 140K
By the time I got enough money to have fun and buy some toys , my body was to old and beyond repair !!!

Flaps? Where are these flaps on a 210? It's not a vacuum problem. Note that the OP is well over a year old. Perhaps his car is fixed.

There is one refrigerant circuit, and a one-piece evaporator in there, so yes, "1 main line for the" refrigerant. The temperature differential is achieved by running the heater core on the warm side, if required.

There is something to the low refrigerant causing a warm left side vent on the 210. Since I can't see inside the parts with the system running, I can only guess as to why this would be so. My guess is that the evaporation is taking place largely or entirely in the right side of the evaporator core, because the left side is full of oil. If it were full of gas, there would be some cooling on the left side, but often there really isn't any.

Another potential problem, of course, is the left side of the duovalve. This should cause problems on the left and right side with equal frequency, however, yet the warm left-side vent on the 210 is extremely common. You almost never hear of a warm right-side vent on this platform. Yet another potential problem which is left-right symmetric is the left-side heater core temperature sensor.