duo valve?
 

I am having an issue with my w210. On a couple of occasions I have had my AC refuse to cool. The situation only lasts a few minutes and then cools great! Today, the other extreme..I tried to turn the heat on..and it wouldn't heat. I turned the climate control to 80 and it was blowing 52degree air. If I pressed the EC botton it would only send outdoor air in the car.

Is this a duo valve(?) problem?
Thanks!

Evaporator temperature sensors are a common problem. I'd start there.

Through the control head you can see the actual values of all the sensors. My A/C article gives the technique and data positions. If you go to the car after it has sat for 24 hours all the sensors should have the same value. This is a quick indicator.