2015 C4GP 2.0HDi EAT6 Exclusive Air conditioning failure

[WillyR]

Good day all,
My trusty 2015 C4 Grand Picasso 2.0Hdi EAT6 Exclusive Aircon has failed - no cooling more than 2ºC below ambient. Immediate suspect is low gas. The Aircon failed under warranty in 2017, and (ALLEGEDLY) the dealer replaced the whole system, piping et al. due to metallic bits in the system.
After very little use since the first lockdown in March 2020 (3400 miles total) with A/C used all the time to keep the seals lubricated etc., I now have no cooling - heating works fine, but that's nothing to do with the A/C.
Googling it, I am about to regas it (2015 onward C4Picassos use the new R1234yf gas, not R134A), but before I do, I need to check the compressor clutch, as it does not sound right.

Every YT Video I have seen says the coil resistance is 3 to 5 ohms - mine is measuring 11ohms, which is regarded in the videos as a failure. I can't hear the clutch engaging or disengaging, and getting to the clutch end of the compressor is a nightmare. It has to be done through the Wheel arch and then the belt cover removed. When starting and stopping the A/C, there is a compressor sound change but no obvious clutch engagement.

Please accept my apologies if this subject is already open, but I couldn't find anything to join or follow. Can anyone help?