First off I am new to the forum and have limited mechanical capabilities. The most mechanical thing I have done was replace the thermostat on my 2011 C-350 and replaced the motorcycle battery (under spare tire)on my 2015 GLK. My current problem is with the a/c on my 2011 c-350 it blows cool but not cold then for no reason starts to blow cold. Dealer stated they thought it was a control module (ECM) but weren't 100% sure and the cost was in the neighborhood of $700-$900 to replace but no guarantee that it would correct my problem. Does any one have any suggestions, or has this ever happened to anyone else?

Thanks
Bill