The first thing to do with most MB's with a EC button is to perform the self diagnostics available at the display.
Read this article to see how and find the appropriate lists of values and codes where ever:
http://www.continentalimports.com/ser_ic40142.html
The service bulletin is for the pressure switch. If it is bad it will show up on the actual values. The most common problem is a bad evap temp sensor act value #5 on most systems. If the value is at 150 or above the compressor won't work.
I have diagnosed this more than once by cell phone with a customer driving his car, just push the buttons and look at the value and stop by when you have a half hour and we'll fix it for you.
The last one I did I diagnosed in the parking lot with the sensor already in my hand. I replaced it and it still wouldn't work and the EC light was on. I have the pressure switch as I have read the bulletin (have never seen the problem but I am ready - buy the evap sensors two at a time). Brought it into the shop and read the pressures turned out the bozo had dumped an extra pound and a half of refrigerant into it before he brought it in. Luckily it only cost him a little extra. He made an interesting problem out of a simple pattern failure. Tripled his bill, he did.