Are you absolutely sure that it's the clutch grinding like that? It sounds to me as if the knocking is taking place in the compressor itself or possibly a weak connection causing the clutch to intermittendly disconnect and engage. If you were getting 10,6 volts reading before and 12 something now, it could be a faulty or corroding connection which is playing games on you. I'd get hold of an automotive stethescope and then listen to all moving parts. I clicked a thumb up on your video, so that you could earn a thousandth of a penny on it for your trouble. I wonder who has been thumbing down your video 8 times. If you allow advertisement in between the video, you could start profitting on it
I probably found the mistake. I was surprised by the remarkably low voltage at the magnetic coupling. Today's measurement: - Onboard power supply with running engine: 14V - at the lower end of the coil: 0.4V (may be correct, there is the pressure switch) - at the upper end: 11,7V This leaves 11.3V for the coil. Thus, a significantly weaker magnetic field is built up. So you get only about 80% of the required force. But where are the 2.3V? If you go your way up in the direction of Plus, you get to the compressor relay. Then you also have the switches in the climate control unit. Then comes the fuse. Instead of 25A there was a 30A in it, which looked a little melted on one side. It doesn't belong in, so 25A is put in. Switched on, let it run, felt again whether the fuse is in the right position and burnt thumbs. The fuse has become enormously hot on one side. So hot that the plastic housing has deformed. I suspect a drop in contact pressure, which has become a problem here. The higher contact resistance ensures that the voltage at the magnetic coupling is too low and warms the fuse. That is one thing. It goes on. The second thing: A current of about 3.9A would fit. Current measurement at the point of the fuse: 5.9A. If someone hasn't fiddled with an additional consumer, it's much too much (the coil should have a resistance of 3.6 ohms). I still have such a compressor. I'll plug it in tomorrow, just let the coil work and take a look at the current. With a little bad luck the coil is gone (short circuit).
I already have new contact springs for the fuse block, but I don't have time to replace them yet. Therefore I built an additional circuit to relieve the circuit from the current of the magnetic coupling. A simple wiring harness, two plugs, a fuse and a relay, it can be removed without any problems. Works perfectly. Thanks for your help in troubleshooting.