main dealers can do it mate, it might be worth going there to start with as they will know where to look right away if its a common fault. sh*tfit will most likely regas, charge u and send u away without making any effort to inspect. Also go careful with an extended warranty to cover you for aircon faults, alot of the time they will argue its damage or corrosion and will try to wriggle out of it, there are some decent warranty compainies out there but there are alot of rubbish ones.