The first time I tried using the A/C, there was no electricity to comp. Fuse OK

Hello, You may or may not be seeking any kind of "codes" for troubleshooting this concern. I would advise seeking a different shop that specializes in heating and air conditioning. the Exxon you speak of might be just fine with many things, but this system may be beyond their abilities. "No electrical power going to the compressor" could mean that there is no signal from the control unit in the vehicle to turn the compressor on. Keep in mind that your air conditioning compressor should turn on almost every time your ventilation system is activated, because even when you are not seeking cold air, it still dehumidifies the interior to make the inside of the vehicle comfortable. In any case, check with one of these trusted folks near you, check this link: http://repairpal.com/mercedes-benz-within-10-miles-of-atlanta-georgia-30346