If the air conditioning system is full of freon however the compressor wont engage where would I need to check for a relay to engage the compressor?

as I understand it There appears to be a air conditioner module behind the radio in the center console which is actually tied in with two other computers onboard and the module is not sending information to start the compressor. Cost as I understand is about , are you ready? Eleven hundred ( $ 1,100.00 ) dollars. Plus labor. At least that is true for a 2003 SL 500. from Mercedes Tech.