Air conditioning compressors turn on and off frequently, which increases the overall load. This is ultimately not good for the health of your entire electrical system as it can lead to arcing and, consequently, an electrical fire. To avoid such situations, AC Boxes are used as a protective circuit against short circuits and overload.
AC boxes are used as control switch to regulate the power supply across the connected device. When the switch is in the OFF position, the device is de-energized (OFF state). In order for it to get power we need to turn on the switch. This closes the circuit and the current flows through the device. So, the function of the ac box switch is to make (switch is ON) and break (switch is OFF) the circuit across the connected device.