The mechanics topped up the gas when they did the last service (done to keep the warranty legit) but didn't go any further with it as they only do the basics. The revs pick up when engaging A/C but thats as far as I have got. Downloaded the R34 manual but it doesn't cover the GTR but will use that as a guide to try and find out more. Might be outside for a while but will check the pipes you mentioned for coolness.
thanks
Edit, the diagnostics from the R34 manual seems to be applicable for the GTR as well, didn't find any faults when diagnosing and changed relays to check it as well so will leave it to the experts as it looks to be a magnetic clutch issue. The tubes from the compressor, the top one was warm and the lower one was normal when the A/C was on.