Sounds like a lack of pressure, which would suggest a leak, or a sticky valve. Is there any sign of a leak on the pipes in the engine bay? If not then can you see fluid in the inspection port next to the filling nozzle by the rad? The main other thing it could be is a stuck expansion valve - these can seize up if the system's been de-gassed for a while, but if yours was working fine before then that's probably not it.
Best off going back to KF, as if it's sprung a leak they should be able to find it.
Thanks for the tips. Not sure how long it was not gassed up for. I only got the car a short while ago. It was completely empty. It did pass the test done and held good vacume.
Where would the valves be located? I have a air hissing sort of noise behind the dash, only when it is switched on though.
To me that suggests low pressure as the system tries to draw in the remaining gas through the matrix - creating the 'whooshing' sound. You'll probably find the it's been de-gassed for a while and one of the O-Rings in the system has dried, cracked and is now letting the AC oil escape after re-gassing. This would explain the symptoms you're getting.
PS - If Kwik Fit start talking big money, or waffle then i'd get a second opinion, as their standard of knowledge is pretty poor TBH.
Went back to kwik fit today and they chap said that it had lost about half it's gas. They have regassed it for free so that was good of them. I have to wait and see now although i guess i have a leak somewhere.
I take it they put some tracer dye in the system to show up any leak? Id'd have thought they'd have put a small amount in in the first place so they could have found it then and there!
No they did not offer that to me. The machine said that my car held a good vacuume but i would say it must have a leak. Anyway it was free this time. If it goes down again i will need to find a air con specialist who can diagnose the fault.