With cold engine off reach down and try to turn the "inner" part of the ac compressor pulley. If it won't turn compressor is locked up. Plan on taking everything apart and flushing blowing out all the lines, evap and condenser. Add oil to compressor, spin by hand on the bench install, vacuum and charge and it should be good to go. Do you know if it was on r12 or r134? Do the ac fittings look to be the same size as say a 1998 E300? If the larger fittings then probably r134.

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Jim