87 300 SDL

Hey guys,
The front end of the compressor moves regardless of where to temperature dial is set ( think this is how you turned the a/c on is these benz wasn't it?) Anyways with no buttons turned on and the fans off the front of the ac compressor moves with the back regardless of where I put the temp at and whehter the a/c is on or not...shouldn't it engage and disengage? What does this indicate I need?