I turned the compressor by hand and it seems to be okay. It turns with a bit of resistance, which I think is normal since it's "pumping" the refrigerant through the system, but nothing is jammed up.

Is there a safe way to manually engage the compressor clutch so I can get the A/C running and make sure the mechanical parts are okay and working? That way I'll be sure the problem is electrical and I can start testing the various sensors/switches.

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1993 300E 2.8