Ok...my car shakes LIKE A MOFO when I have the A/C on and I'm in neutral or have the clutch disengaged and whatnot. I'm not too familiar with A/C's...so I'm not sure what it would be. Maybe an unbalanced pulley or something? Sometimes it shakes pretty bad when I take off at low RPM's too.

 

Park the car, leave the engine idling, with the AC turned on, open the hood & look. You aren't gonna pin down the location of the problem from the driver's seat.

Wait for the AC clutch to engage, then watch the AC belt and it's pulleys. They shouldn't wobble. For that matter, the compressor shouldn't wobble on it's brackets.