What is a window air conditioner? A 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.The capacity of an AC, or its cooling ability, is based on its tonnage. However, split ACs are mounted high and designed for cooling larger spaces, whereas window ACs are better for air circulation in smaller rooms. Further, it is possible to get split ACs of a high tonnage, of above 2 tons.