Yes that would be normal procedure but garages were closed on Sunday and Halfords shops only do filling from a DIY kind of kit from a small bottle.
Anyway dropped car 8am Monday morning at local garage and collected Tuesday morning 8am. They checked all lines, joints and parts that are accessible for signs of UV dye leak, did not find any so either no leaks in any visible places or no dye has been added in previous fill ups. Then did extended time nitrogen pressure test, then vacuum test and after finding no leaks finally charged it up also adding UV dye to make easier to find any leaks in future. Wallet is £64.80 lighter but S4 now has fully working AC.
I know I could have had it re-charged cheaper especially with Groupon coupons but these days I have no time to mess a around, wait for booking and drive the distance so for the £30 or so quid I could have saved I chose to save my time.
Saturday night when wife and kids returned from holiday she said she was not impressed with my purchase and said I have wasted money for old 'junk', calmed down a bit when I explained that I got it at reasonable price with a look at selling it at higher price and enjoying car in process for a while and have already fixed biggest flaw - the non working roof. Somehow Sunday she could not wait to get behind wheel and later to go round friend houses to show off.
She was also disappointed Monday morning that I have taken car to garage and she could not drive it to work.
She took it to work this morning and was picking up colleague who's car had starter motor broken down so I suggested she should seize the opportunity plug it for sale.
The answer was : "Sell A6, I want to keep this!".
She's becoming addicted to the sound of Mliltek.