Gave up and took it to the shop today, refrigerant was slightly low (1.7 instead of 2 lbs) but he didn't think that would be enough to cause the clutch not to engage. He tried jumping it and whacking it with a rubber mallet too, to no avail. Checking the resistance just between the wire and the front of the clutch without taking it apart he thought it had a short in it, and that it would be less labor and a better chance of a long-lasting fix to just replace the whole compressor rather than trying to replace just the clutch/coil. He didn't think it was extremely likely that I'd caused it by pulling on the wire since it's clamped down pretty good by the coil but he couldn't 100% rule it out.

Talking to Mike @ Midwest he said that sometimes when people convert R12 to R134 they use the wrong kind of oil and it burns out the clutch faster. I wonder if that's what happened here b/c the last time it consistently worked I ran it for several hours in one go, whereas I only ever remember running it for <20 mins at a time before.

The adventure continues...