On the automatic climate control module of my C280, there is a switch that turns the AC compressor on and off ("EC" or ecomony). In the winter, i usually leave it in the off position, and the red light is on. Today I tried to turn the AC on, but nothing happened and the red light switch stayed on. The ambient air temp was about 45 degrees F, so maybe if the compressor doesn't kick in due to low outside air temp, the red light stays on. But I think in the past, it goes off and on when i've pushed the switch.
Could this indicate a problem with the AC system?

 

Yes, the EC light will stay on if there is a problem with your compressor. Usually it's good to run the AC once a week or so for a few minutes during the winter.

You can check the codes and values via the Climate COntrol read-out... but that's another story! What year is your C280?

 

I'm having the same problem with a 1998 C230 W202 I did the recirc/up-temp(red)/rest switch test and the control panel displays 01. Does this indicate a bad interior temperature sensor?

 

i've had to replace the climate control cause the pressures were still good. . 800 dollars later you can have your compressor go on.

 

I found it! it's my condenser that's leaking the green dye is coming out everywhere on the passenger's side. It seems that it is just corroded out, anyway I've got a new one ordered along with a new drier.

 

Its spring time and everyone is discovering that their AC doesnt work. i will also be having a die test done soon. Ran the diagnostic and found that my refrigerant is LO . cant wait to see where the leak is!