Air conditioner problem

I have a 2001 E46 325ci and we have a hot days in perth, I want to be sure that it is a Final Stage Regulator problem. When I start my car the aircon comes on as normal, after 10mins the aircon cuts out for about 2mins, then comes on, then off. this lasts for a while. By that stage I have the windows down and its no good when ht e outside temp is 40 deg. Last summer it was fine, I has new gas put in and a check onthe compressor, it sounds like everything is on i just cant get a consisitant cold air.