My 03 E500, 33k miles, has an odd ball problem with the climate control. Start the car first thing in the morning, turn on the A/C, take off and for the first 30 or so miles, all is well. A/C blows cold front and rear...no problems.
After about 30 miles, the rear A/C is blowing HOT. Front A/C is normal. This happens without fail now and just happened out of the blue, wasn't intermitant.So of coursethe center console gets really toasty and veryuncomfortable. I can close the rear vents, but that doesn't prevent the flow of hot air through the ducts in the console, since the air flow is controled by the fan speed in front.
Any ideas? Is a vent solenoid stuck, or is the climate control computer screwed up? Anyone know what controls and facilitates hot/cold air to the rear compartment?
I rarely drive this car and I'm wondering if the lack of use, is making things stick/malfunction.

 

I don't have the layout of the 211 model,however on the earlier systems you can run the onboard diagnostics program,give it a try and see what it reads
http://www.eclassbenz.com/node/27
if it works on your model post the values and errors you get.
Sounds like a stuck duovalve,sometimes a firm tap with a screw driver handle will free it up.
could not find a good picture of the duovalve and on the link it is for a british car so it is mirror imaged i.e. yours is on the passenger side up by the ecu/tcu.just give all of them a firm drum like whack with the handle of the screw driver while the a/c is on full for all areas of the car,the a/c system on the benz are shared systems.So if the valve is stuck it will send hot water into the system thinking it is calling for heat.
keep us posted