A direct expansion air conditioning unit, also called a DX unit, cools indoor air using a condensed refrigerant liquid. DX air conditioning unit is the most commonly used system in homes in United States.
A split air conditioning system puts the compressor and condenser outside the building and the evaporator and fans inside the building. In a central air conditioning unit, fans push cooled air from a centrally located evaporator through ducts to the entire building. In a ductless split system, fans that are mounted on wall move the air from the evaporator into the room.