To start with; yes my car still has all the hardware, no it hasn't actually blown cold since the 2000s, yes I want to get it working again, yes I like a challenge.

Years ago I bought a pair of apparently good hoses for a 6 from the forum - those ones that normally corrode and leak the refrigerant. I stored them for years and fitted them in 2021 along with a new condenser, receiver/drier and many O rings throughout the system. I didn't get further at that point and left it on my 'to do' list.

The day has come and I hope someone can help with some compressor-related specifics.

I've had the compressor off to look over it and change the bearing as part of preventative maintenance. On top of the compressor there is a 17mm oil fill/drain plug. No oil drained out of mine when I turned it over although looking through the drain hole the inner pistons/mechanicals all look clean and shiny. I can see the compressor internals move when I turn the pully, it feels smooth and good pressure is observed at the rear ports.

Shouldn't the compressor have oil in it? Is the rest of the system also suppposed to have oil in it, mixed in with the refrigerant? Are these different oils or is it the same oil that lubricates the compressor and the wider system?

The compressor on a 6 (at least my P3) is a Sanden SD7V16, model number 1227F, and is common to other PSA vehicles of a similar vintage. It says it wants an SP-10 oil but this seems uncommon and research indicates this is equivalent to widely available PAG 46. I bought 250ml of PAG 46.

Research also indicates that the compressor (or entire system?) takes ~120 to ~140ml of oil. Do I just chuck all of this into the compressor fill hole?

Some YT videos I've seen (of totally different air con compressors on different cars, admittedly) show about 20-50ml draining out of the compressor. With this in mind, does ~140ml seem plausible?

After sorting the oil, I propose to use a vacuum pump to test the system before filling with refrigerant.
I live in hope of being the only 6 with working air con in the entire world.