Today's service call was for an AC that wouldn't turn on outside, even though the thermostat was running. After checking the low voltage signal, I inspected the outdoor unit's electrical components and found the problem: a burnt-out and pitted contactor. This small switch is essential for sending power to the main components. I solved the issue by replacing the old contactor with a new, durable one. As soon as I restored power, the outdoor unit kicked on perfectly and started cooling the house.