Many of us didn't grow up with air conditioning, so we're not familiar with the various components that make up a central air conditioner. We're used to fans, from small ones that sit on a desk to floor models and ceiling fans that are very popular, especially in southern states.
That means buying a new air conditioner is more challenging with new concepts and terminology to learn, so you can make decisions with confidence. And even if you're familiar with one type of air conditioner, there are times when you'll have to learn about a different type of air conditioner which happened to me.
We've used whole house fans for many years in the northeast. That's why I'm learning about central air conditioning now that we own a house in the desert near Phoenix, Arizona. We have a heat pump which provides air conditioning in the summer and heat in the winter. When heat pumps are installed on the roof of the house (the installers didn't think our town allowed this), the entire system is integrated.
Our central air conditioner is called a vertical system because it stands up, where attic and roof installations lay horizontally.
Anatomy of a Central Air Conditioner
When you look at your HVAC system, you only see two boxes – one that sits outside your house, and the other inside your home in the garage, attic or basement. The outside components box is called the condenser while the inside box is the air handler. But you need to understand what's inside these boxes, to learn how your central air conditioner works.
Here are the key components (numbered above) making up any HVAC system, with a brief description of what they do. To help you get a better view, there are also photos of each component taken during the installation of my new heat pump.
- Evaporator – super cool refrigerant flows through the evaporator coils and removes both heat and humidity. The heat is absorbed by the refrigerant and PVC piping takes the water removed from the air. The water drains outside using gravity or in some cases, a pump.
- Blower (or fan) – pulls the air from your house into the air handler where it circulates the air over the evaporator coils to cool it (or heat it when you have a dual purpose heat pump). The conditioned air moves upward and out to your house through the ductwork.
- Condenser – has coils around the outside of the box to circulate the refrigerant from the air handler. The heat absorbed by the refrigerant is then released into the outside air, which is why this box is always found outdoors.
- Compressor – is the heart of your HVAC system, pumping refrigerant through the closed loop between the evaporator inside and the condenser outside your home. The refrigerant changes between a liquid and a gas, moving heat between your house and outdoors.
- Outside fan – blows air over the condenser coils to release (in tech speak, the word is dissipate) the heat into the outdoor air for air conditioning. When a heat pump is operating in reverse, the same refrigerant absorbs heat from the air and it moves inside to heat your home.
- Return air grill and filter – intake vent has a grill and inside a filter to prevent objects in the air from clogging or damaging the components making up your system. The reason you need to replace the filter frequently is to make sure enough air reaches the air handler, so your HVAC system runs efficiently.
- Thermostat – mounted on a wall in your house, monitors air temperature and depending on your settings, sends a signal to start or stop the HVAC system from operating.
- Line set – refers to the pair of copper refrigerant lines running between your condenser and evaporator coil, located inside the air handler cabinet. They're different sizes (set by manufacturer) and only the larger suction line carrying refrigerant as a vapor needs to be insulated. The smaller liquid (state of the refrigerant) line does not need to be insulated. Confused? Here's a video on Refrigerant Line Set Sizing.
- Condensate drain – is the white plastic (PVC) pipe that runs from the evaporator coil to a drain using gravity or a pump.
- Plenum and ductwork – The plenum is the metal box attached to the supply outlet of your HVAC equipment, that distributes conditioned air to the ductwork. The ductwork distributes the air to individual rooms of the house.