Window air conditioner is the simplest type of AC unit. It’s a single unit with all of the parts and components contained inside one box or casing. This type of AC is usually mounted or installed in a window and plugs into a traditional electrical outlet. It is designed to be installed in a window to cool a room or small area. It works by drawing in warm air from the room, cooling it using a refrigeration system, and then releasing the cool air back into the room. The warm air is vented outside through the window.