[carlos80]

Could be the relay,maybe under/over charged, a/c pressure/cycle switch. If you really want to keep it buy a manual and read up on the do s and don't s of working on your a/c system and try and figure it out yourself, or take it to a good a/c shop, because if the one you've been taking it to doesn't know where the compressor relay is at that tells me that they're either lying to you and just want to get rid of you, or they don't know what they're doing.