It's common to assume low refrigerant is the cause for excessive clutch cycling and this often leads to adding refrigerant and thereby overcharging the system. Most vehicles have a compressor clutch cutout strategy based on an engine coolant temperature of 220 - 240 degs F. The vehicles computer relies on a coolant temperature sensor to provide the signal for the compressor clutch decision and if the sensor reads too high the clutch will cycle off. Cooling systems with a 50-50 anti-freeze mix and the proper radiator cap should boil at around 275 degs, so the system may not be boiling when the compressor cuts out. Check the actual coolant mix and temperature by using an Infrared thermometer to check coolant temperature and a Scan Tester to tell you what temperature the sensor is actually signaling to the computer.