A failing AC contactor usually shows up one of two ways. Either the unit will not turn on at all when the thermostat calls for cooling, because the contacts are too pitted or burned to pass power, or the unit will not turn off, because the contacts have welded together and stay closed even when the thermostat is satisfied. Other signs include a loud humming or rapid chattering sound from the outdoor unit, a buzzing that comes and goes, or you open the panel and see the contactor's contacts blackened, pitted, or melted. Sometimes ants or debris get inside and jam it. The contactor switches thousands of times each season and is a normal wear item, so failure is common, especially after several hot Los Angeles summers. It is an inexpensive part, but it carries 240 volts, so do not poke at it. If your AC runs nonstop or will not start, call LA Heating & Air at (818) 660-1062.
