Steve - The clutch would not engage. I either had a faulty clutch, was out of refrigerant, or had a faulty low pressure switch.
A pro at http://www.aircondition.com
helped me out. He told me that Accords were notorious for faulty low pressure switches. In my case the R-12 leaked out where the switch fastens to the receiver-dryer, so I had a bad switch and no juice.
The tech had me pull the switch connection, then jumper it with a wire turned in a u-shape. The A/C switch on the dash had to first be activated. The clutch engaged. You do not want to engage for long if you're dry. This does narrow down the problem. Once engaged, I saw no gurgitation in the sight glass, especially upon activation of the clutch. I was sure the juice was gone as was the switch.
I haven't dealt with this on a Benz yet, but I suspect the process is similar