New to the forum and this question may have been asked previously but after searching I finally gave up and decided to ask. I own a 2011 C-350 (W204) with an A/C problem, I'm hoping somebody has run across the same problem and had a simple fix. The AC blows cold air sometimes and for no reason starts blows ambient temperature air. Could it be the Evaporator Temperature Sensor (Switch). Or does anyone have any additional information that would help me solve my problem. The local dealer said they thought is was the AC modem (the brain that talked to the AC system) and quoted a price of around 3,000k and didn't guarantee that would fix my problem. Everything works perfect when it works so cold you have to turn it down. Any suggestions or help would be greatly appreciated.

Thanks
Bill