In the world of air conditioning, the evaporator (commonly referred to as the indoor unit) does two things:

• In cooling mode, it converts refrigerant liquid to gas in order to absorb heat from the air
• In heating mode, it converts refrigerant hot gas to liquid in order to release heat to the air

This is the underlying method in which all air conditioners are able to provide reverse cycle conditioning, allowing them to either heat or cool depending on your comfort needs.