I've got one sucess story on my 300E. Vent temps would cycle between 49-54F regardless of outside temp - the ETS was turning the compressor off WAY too soon. I checked the ETS readings with a VOM and a digital thermometer (stuck both into a vent in my house A/C system) and found that the sensor was in spec, but on the far side (warm) of the allowable tolerance. (I think it was 17.5k at 15°C, or something - cant' recall exactly). I installed an 82k ohm resistor shunt, which pulled the ETS resistance readings to the other (cold) end of spec, actually a little outside of spec but not too far (dropped to 14.5k, I think). Now my vent temps cycle from 37-42F, which IMO is perfect.
My 300D is bone stock (no ETS modification) and cycles between 38-42F with R-12. My E500 is also stock but cycles between 42-45F with R-134a. Mercedes says the vent temps should never get below 5°C (41°F) but I believe that's too conservative. I don't think pushing the temps near freezing is wise, but getting the system to the high 30's (F) shouldn't be a problem. I'm going to test the resistance readings on the ETS in the diesel when I pull the dash next time, and I also want to install a resistor shunt (but about 100k) in the E500 to drop the temps a little.
If you're not getting low 40's vent temps, you're not getting proper A/C function.
