Reverse cycle air conditioning is a type of cooling system where the refrigerant undergoes a process whereby it is circulated in the opposite direction compared to regular split-type or window systems. This means that instead of bringing heat from outside and dumping it inside, like in standard HVAC systems, an indoor unit (evaporator) absorbs heat from indoors and transfers it outside.
As such, the process is reversed, during summer months when we need cooling, we hook up our units to expel heat into hot climates, come wintertime we turn on the heat pump with the intention of sucking cold air and pumping out warmth for cozy indoor environments. The key component in all heating and cooling systems, be they central air conditioners or window units, is something called a refrigerant.