Capacitors are devices that store an electrical charge. They’re used in a variety of applications, including in electric motors and AC units.
When an AC unit is turned on, the power needs to travel through the capacitors in order to start the electric motors. If the capacitors start to lose power, the AC unit won’t work as efficiently.
Home Depot doesn’t sell capacitors specifically for AC units. However, they do have a variety of other AC power supplies and components available for purchase.