OK so I keep getting CA120-64 fault, and have a replacement compressor on order. I Received my iid tool today and started looking into the issue
First of all I deflated the resevoir and refilled it upto 220psi /1500kpa, this took roughly 10 mins to fill. Once it hit 220 psi the compressor stopped and the gallery pressure immediately dropped to 34.8psi / 240kpa. I then sat and waited another 10 mins and it was down to about 220kpa when the compressor kicked in and it immediately jumped back to 1500kpa

1.Am I right in thinking there must be a leak between the compressor and tank
2. Can anyone give me more tests I can do with iid tool to pinpoint it.
3. Is 10 mins too long to fill the resevoir

check the air tank. they rot out along the seam that sits nearest the chassis. some bubbly water and a brush will help

A stuck compressor exhaust will cause similar issue. 2009 Range Rover Sport Supercharged