IF indeed the system IS charged correctly, a restriction may be causing the High side switch to cut off the compressor (High pressure limit), however this is not very common.
Most of the time if the compressor is cycling on and off it is due to a low freon level, causing the low pressure limit switch to shut the compressor off as the pressure drops below a certain point. Then once the compressor shuts off, the level on the suction side rises back up, and it turns back on.
For both of your situations, I would suggest it is a slow leak somewhere. If you have the know how and equipment, you can check with gagues to see the pressure and how it reacts when the compressor is on, (Checking/Monitoring both High and Low sides) but unless you are well educated on the use of the equipment, the potential hazards, and the EPA laws, it is best to have a professional work on the AC system. The professional may also save you a lot of time and money hunting down the leak to solve the problem.
