The AC is only blowing hot air. The compressor is not switching in normal operation, neither does it engage when you hit the compressor switch on the control panel. It however will engage and operate on a separate live feed.
Had the system regassed but no change in compressor behaviour although blowing slightly cooler.
The regassing took longer than usual (apparently) the AC gassing guy thought that there might be a blockage in the system

Any ideas?

 

Have you run the climate control diagnostics on the head unit? Any errors there? If you're not sure how to run the diagnostics, this this link:

http://www.audiworld.com/tech/int5.shtml

 

Thanks for ths suggestion. I will give it a try.