steveeeee

I had the system re-gassed (special offer £20, so worth a try as a troubleshooting step). They said it wasn't completely full before they started but it wasn't terribly low either. The purple wire seems to disappear under the engine bay fuse box and I can't tell where it comes out. Does anybody here know where it goes to? I'd really like to check continuity first before I start chopping things up.

I have the exact same problem! From what I've read, the most likely culprits are either a break in the purple wire leading from the fan controller (see here and here) or a faulty G65 pressure sensor (not 100% sure yet if the mk3 has one) (see here and here). I also get no error codes on my ODB2 reader using Forscan, but apparently this is quite common as a number of air con related faults don't throw errors. Next time I have a block of time (difficult with 3 kids!) I want to try and find the other end of the purple wire so I can do a continuity test with a multimeter.