Not sure why you think the refrigerant level is good. But your problem as described is "most likely" low charge due to leak or bad LP switch. The easiest way to check to see what pressure it is cycling is with a gage set, more specifically the LP gage. It should cycle the compressor off at roughly 25 psi and back on again at about 45 psi (specs vary a bit for different car models). If it is cycling around these numbers but rapidly I would suspect a low charge. If it is cycling off much higher then 25 psi the LP switch is probably defective.
There is no foolproof way to get the charge exactly right except but evacuating and refilling with specified amount, but you can get pretty close with some practice and experience. There are lots of variables to play with and a car system is never truly at a steady state like a residential unit, hence the difficulties in diagnosing charge. Get some gages and read this: