A Direct Expansion (DX) 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 across the United States. 

Air heat pumps beside house

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. 

Find out more about Split Systems in this article and this infographic from energy.gov.

How Direct Expansion Units Work

The unit cools air bypassing the condensed refrigerant through a heat exchanger inside the building to be cooled. In this part of the unit, called the evaporator, the refrigerant expands as it absorbs heat, eventually converting to a gas.

The unit then pumps the refrigerant to a compressor, which compresses the gas and passes it through another heat exchanger, the condenser, outside the building. The heat that has been absorbed by the refrigerant is released to the outdoor air, and the cooled, compressed refrigerant is once again in liquid form. The unit pumps the cooled refrigerant liquid back to the evaporator and the cycle begins again.


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