Finally re-installed all the stock AC components. Which terminal on the A6 compressor is the ground terminal? Assembly manual shows the terminal furthest from the engine, service manual shows terminal closer to the engine. Is there a way to test for this? There seems to be continuity between the two terminals, and no continuity from either terminal to ground, so perhaps it it can be either one?
The terminals on the compressor clutch should have a little barb that only lets you install the plug one way. That's why the connector has notches on one side.
In any case, the compressor clutch is just an electromagnet. Wired one way it pulls the clutch plate in and engages the clutch. Wired the other way, it pushes the clutch plate away. If the clutch doesn't engage, reverse the wires. You can't hurt the coil in the clutch by doing that.