Main floor system condenser making a noise, on arrival turned thermostat on and found that Contactor opening and closing, Contactor coil was good 19 OHMs, found that system had a module for fresh air damper wired in and has gone bad causing Contactor to open and close, unwired and checked system and the clicking stopped, checked pressures and it does appear the system is 1 to 2lbs low on charge homeowner wanted to hold off on refrigerant and see how system does.