HVAC Basics : Components of the HVAC Unit

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HVAC Basics: Components of the HVAC Unit

A properly functioning HVAC unit should heat, cool, dehumidify, humidify, clean, ventilate, and control air flow. It’s in charge of anything that has to do with air within your home. With all of these capabilities, the interior of your HVAC unit can feel like the Enterprise’s engine room. However, the basics of the HVAC are actually quite simple–and once you learn what each part does, you’ll be better able to diagnose any problems or concerns you might have with your system. 

Most of the parts below are present in every HVAC system. But a couple–including the parts that live outside of your home, as shown below–are present only in split systems. (Chances are that you do have a split system, but if you don’t, some of these parts will not be present in your HVAC unit.)

Image of an external HVAC unit.


Clipart of a thermostat.The thermostat–which you’re presumably familiar with–controls the whole system. It is usually found in a central location and can be programmed manually or remotely (in some cases) to heat or cool according to your preference. If the temperature in the home then rises above or falls below the set temperature, the thermostat prompts the rest of the HVAC system to start up.


The furnace is the most essential part of your HVAC system. It is often stored in the basement, attic, or a specified closet. The furnace is involved in both heating and cooling processes, but its primary purpose is to heat air. It can get this heat from various sources, including solar energy, heat pumps, electric resistance, and combustion. 

Heat Exchanger

Clipart of a heat exchanger.The heat exchanger is found within the furnace. and is what the thermostat switches on in the cooler months. The heat exchanger pulls in outside cool air and heats it within the furnace so that the heated air can then be sent through the ducts and vents.

Evaporator Coil

Where the heat exchanger warms air, the evaporator coil cools it. Located on the top or side of the furnace, the evaporator coil uses the furnace’s blower and refrigerant to cool air that will then be transported through the ducts and vents to keep your home cool and comfortable in the summer.

When the refrigerant absorbs heat, it cools the room and becomes a gas. When it lets off heat, it heats the room and becomes a liquid. So if it’s cold out, the refrigerant absorbs what little heat there is and emits it inside. If it’s warm out, the refrigerant absorbs heat from inside and emits it back outside. 

The evaporator coil is what allows the refrigerant to transform from liquid to gas, thus cooling the room.

Clipart showing the three functions of an HVAC unit.

Condensing Unit

The condensing unit is the part of your HVAC system that is outside the home. It connects to the internal system through a vent. The condensing unit holds refrigerant, and is essential in allowing the refrigerant to transform from a gas to a liquid.

After passing through the condensing unit, the refrigerant is then pumped to the condenser coil.

Condenser Coil/Compressor

Clipart of an HVAC condenser coil/compressor.Inside the condensing unit there is a condenser coil or compressor. The main function of the condenser coil is to remove heat from the home into the outside air. It does this by compressing the warm refrigerant gas into a cool liquid. 

The refrigerant then begins the heating/cooling process again.


Clipart of a fan.The fan is found on the condensing unit. It blows over the condensing unit compressor/coil to disperse heat and cool the refrigerant faster.

Refrigerant Tubes

The refrigerant tubes (or lines) carry the refrigerant gas from the evaporator coil to the compressor and the refrigerant liquid from the compressor to the evaporator coil. 


The ductwork includes the “tunnels” in your house which allow air flow. They’re often made out of aluminum, and carry the heated or cooled air through the home to the vents so that the air can be evenly dispersed throughout the home.


Just as the name suggests, the filter for you HVAC unit removes impurities from the air. The filter may need to be replaced every 1-6 months, depending on your system. 


Air needs to get into your home somehow. Vents connect the ductwork running through your home to the outdoors. 

These are the most essential components of your HVAC unit. If an error occurs, knowing the function of each part should help you to pinpoint the problem.











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