An air conditioning technician should discharge the refrigerant. Then, they should unplug an electrical connector from a pressure cycling switch. A backup wrench should be used to unscrew the pressure cycling switch without deforming the pressure line. The O-ring of the switch has to be lubricated with clean refrigerant oil of the proper kind. The new one has to be screwed into the threads and tightened well enough. After that, you are supposed to reconnect an electric connector. Finally, it is the duty of the shop which discharged it to evacuate, charge and leak-test your system again.