The cycling is normal if the demand on the a/c is not very high - i.e. if the outside temp is not especially hot. If it is very hot outside the system will normally need to run all the time to produce enough cold air. If it is hot outside and you are not getting good cooling and/or the compressor still cycles, the system is likely low on refrigerant. In this case it is cycling when the pressure gets too low, to protect the compressor. If there is enough refrigerant then the pressure should never fall low enough to shut off the compressor (again assuming it is hot outside). The pressure readings you have do not seem far from normal. The reading you get with the compressor running continuously should be in-between, like 30 psig, if there is enough refrigerant.