How Does a Central Heat and Air System Work?

A central heat and air system with a heat pump provides year round comfort by maintaining desired temperatures inside the home. It cools the air during the summer and heats it in the winter. An air conditioning system works in the same way as a refrigerator, cooling an entire room or home instead of just a small box.

• The cooling begins when the thermostat, sensing too much heat in the room, signals the compressor to turn on.


• A chemical refrigerant, usually Freon, is pumped into the compressor as a cool gas. The compressor spins the gas, applying pressure, until it becomes very hot.


• The hot gas passes through the condensing coil, which allows the heat to dissipate. When it reaches the end, it has become a cool liquid.


• This liquid remains under a lot of pressure and is forced through the expansion valve, which is a tiny opening that allows only a small amount of the liquid through at a time.


• As the liquid passes through a second set of coils, it starts to evaporate. The evaporation pulls the heat out of the air around the coils, cooling it.


• A fan blows this cooler air through a series of ducts, while simultaneously pulling the warm air from the room.


• The refrigerant has once again become a cool gas and travels back to the compressor to start the process over again.


• By switching the central air conditioning system to heater, the heat pump performs the opposite function and heats the air in the home instead of cooling it. This is accomplished by reversing the flow of the refrigerant, allowing the cool air from the room to be drawn into the system and warmed.