I had an Air Con problem with my A4 and got it repaired by a local Refrigeration specialist...a one man business and he didn't charge the earth. Check out Refrigeration Services in the Yellow Pages. No use me giving you this man's name unless you're in Northern Ireland.
Mine has packed up aswell, it still blows but only hot air - apparently there is a leak somewhere in the system as when it is re-gassed, it keeps escaping.
we had that problem & when they looked at re gassing, we were told we would need a complete new unit... not worth it £900 at the time, besides the best air conditioning open the windows..... lol