I finally tried another method to fix it. It's a bit of a hack which can easily burn out the magnetic clutch, but honestly I'm never going to properly fix the A/C, so would rather have done this, and if it breaks again will give up.
I used a DC-DC converter to increase the voltage being fed into the magnetic clutch. This will increase the strength of the electromagnetic pull-in. I used the following specific device: DROK 150W DC Boost Converter on Amazon. It's available on Amazon.ca as well.
If you have time you can order from Aliexpress for $4, but I wanted prime shipping so paid the extra fee. The device isn't really designed for automotive use so it seems likely to burn out from heat. I'd check it occasionally and watch for the capacitors to buldge out, keep an extra 1 or 2 of them on-hand to replace.
Once you've got this, it's a simple process:
- In the front fuse box, find the grey wire. Cut the wire - the part coming from the relay goes to the "IN+", do not connect the "OUT+" yet!
- Connect the ground wire ("IN-") to a grounding point near the fuse box. I couldn't find an easy ground in the box.
- Power up the system, and turn on the A/C. The green light should come on. Measure the output voltage and adjust it down to about 15V.
- Turn everything off, then connect the "OUT+" to the grey wire going out.
- Replace the input fuse on the board with something smaller (default is 15A), I'd go for about 5A-8A and see if it doesn't burn out.
I measured quickly and it seemed the normal current draw on the clutch was about 3A (at regular car voltage).