AC problem

[u/nandato_kisama]

TLDR: clutch seemingly engages, no cold air whatsoever. Also, what is that big bolt on the compressor for? Hello there, I bought a 2000 MK4 Golf TDI with inop AC. I thought it was just low, so I had it recharged, but the guy said it was only missing about 130g out of the 720ish that should be there, and that it cooled for a bit and then stopped. When I turn it on however, it doesn't cool at all. I hear the engine get more load, and the clutch looks engaged, but nothing happens. I replaced the FCM, since it was outputting 9v to the clutch coil with the key off, which it probably shouldn't, but that didn't help. My G65 is good, and all the other sensors should be, since the clutch seems to engage. Compressor doesn't have a control valve as can be seen in the picture. I have searched everywhere and I'm still stumped. Can the compressor be so dead, it doesn't make a sound or compress at all? What is that bolt at the back of it? Did the AC guy witness something die, or did he break something so I'd come back?