70/05 stang

I have a 67 coupe with a air cond that was installed by the dealership clear back when. Anyway I just had it charged with freeze 12 put 3 12oz can in and 2 small cans of oil charge. The problem I am having is that it cycles on and off about every 15 secs when above 2000 RPM and at idle it works good.The head pressure is 350 so don't want to add any more freeze 12. Any ideas what I need to do next.