air conditioner units outside of home

Although there are various parts of an air conditioner, four main components keep your air conditioning unit operating like a well-oiled machine. They are the evaporator, condenser, compressor, and expansion valve. Each of these components functions in sync and has a specific job of providing cooling comfort for your home.

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The Most Important Parts of an Air Conditioner and Their Functions

The most important parts of an air conditioner are the evaporator coil, compressor, condenser coil, and expansion valve. Each component is part of a circuit connected by refrigerant tubing and plays a pivotal role in cooling your home. When one element ceases to function, the entire system goes down.

1. Evaporator Coil

The evaporator coil is attached to the furnace or contained within the air handler. The coil typically has an A-frame shape with two panels of thin, metal fins. The fins allow air to pass through to the refrigerant tubes. The tubing is made of heat-conductive metal such as copper, steel, or aluminum and bent into a series of U’s.


The evaporator coil’s role is to absorb heat and humidity from your home’s air. Cold refrigerant flows through the tubing while warm air from the house passes over the coil. The refrigerant absorbs the heat and humidity from the home’s air, and a fan blows the cooled air into the home through the vents. The warm refrigerant then flows outside to the compressor.

2. Compressor

The compressor is often referred to as the “heart” of the air conditioner because it pumps refrigerant through the air conditioning system. The compressor is located inside the condenser unit. The compressor receives the refrigerant after it has absorbed heat from the home’s air. At this point, the refrigerant is a warm, low-pressure vapor. The refrigerant will eventually circulate back inside the house to repeat the heat-removal cycle, but first, the refrigerant must be returned to a cold, liquid state.


The compressor performs the initial step in the cooling process. It applies energy until the refrigerant becomes a hot, high-pressure vapor. Using heat and pressure on the refrigerant serves two purposes. One, the refrigerant must be heated to a temperature higher than the outside air to release heat as it travels through the condenser’s coils. Two, pressurization allows the refrigerant to flow smoothly through the coils. After the compressor heats and pressurizes the refrigerant, it flows to the condenser.

3. Condenser Coil

The condenser coil releases heat the refrigerant has removed from the home’s air. The condenser is the central unit located outside the home. It resembles a box encased in thin metal fins. Beneath the fins, the surface of the condenser is covered in coils, usually made of copper.

The compressor releases hot, high-pressure refrigerant vapor into the condenser. The refrigerant moves through the condenser coils while the fan supplies cool air. The fan’s air cools the refrigerant in the coils, and the metal fins conduct heat away and into the outside air. The refrigerant condenses as it cools, becoming a liquid. The refrigerant flows to the expansion valve next.

4. Expansion Valve

The refrigerant enters the expansion valve after leaving the condenser coil. The valve reduces the refrigerant’s pressure, cooling it further. Once the refrigerant returns to a cold, liquid state, it can return to the evaporator coils to cool the home’s air and continue the cycle.

Other Air Conditioner Components

Your air conditioner contains other necessary components besides the four main parts. The air filter, refrigerant, fan, and thermostat are four more essential parts of the cooling system.

man changing out central air conditioner filter from return vent

Air Filter

The air filter filters out particles in the home’s air, such as dust, pet hair, and pollen. Every homeowner should know where the air filter is located and which filter is compatible with their system. The air filter must be changed regularly to maintain the air conditioning system. How often to change an air filter depends on the filter's quality, but they should typically be changed every 30 to 90 days.

Fiberglass filters are the cheapest but are also low-quality and must be changed every 30 days. Pleated air filters are of better quality and can be changed as little as every 90 days, but they are more expensive. Washable filters are relatively cheap, but they have a low rating regarding how well they trap small particles. In addition, they have to be carefully washed to avoid damaging them and thoroughly dried so they don’t grow mold.

The air filter's location varies depending on the type of HVAC system, but it can usually be found in the return air duct or blower compartment near the air handler.

410A refrigerant for air conditioning units


Refrigerant is the chemical that cools the home’s air. The refrigerant flows through the air conditioning system in copper or steel lines: the temperature, pressure, and state of the refrigerant change throughout the process. The cold, low-pressure liquid refrigerant absorbs heat and humidity from the air inside the home at the evaporator coils. In doing so, it changes to a gas. The refrigerant then flows outside to the compressor to be pressurized and further heated. Heat is removed from the high-pressure refrigerant as it flows through the condenser coils. The expansion valve reduces the refrigerant’s pressure and cools it to a liquid. Then, the refrigerant flows back into the home to repeat the process.

Refrigerant, also know as AC Freon, is a potentially hazardous chemical. If a refrigerant leak occurs, a professional HVAC technician should be called immediately. Only licensed professionals can handle refrigerants.

central air conditioner blow fan and condenser fan illsutration


Air conditioners typically have two fans, the blower fan and the condenser fan. The blower fan is indoors and blows cool air through the home via the ducts and vents. The outdoor condenser fan helps remove the heat the refrigerant has absorbed from the home’s air.

central air conditioner thermostat


Like the air filter, the thermostat is a component with which homeowners should be familiar. The thermostat uses sensors to maintain the temperature of the home. It typically has switches to turn on and off the air conditioner, the furnace, and the blower fan. Homeowners can set the thermostat to their desired temperature, and the thermostat will cycle the air conditioner on and off as often as necessary to maintain the temperature.

How does an air conditioner work?

An air conditioner’s various components remove heat and humidity from the air inside a home and release the heat outside. The refrigerant, evaporator and condenser coils, compressor, condenser, expansion valve, fans, air filter, and thermostat are essential in cooling a home’s air.


The main parts of the air conditioner exist in a circuit connected by tubes of flowing refrigerant. When the thermostat senses the temperature is higher than the temperature at which it’s set, it sends a signal to the compressor to begin the cooling cycle. Refrigerant is in a cold, liquid state when it flows through the evaporator coils. The refrigerant absorbs heat and humidity from the home’s air. The blower fan blows cold air throughout the home’s ducts and vents while the air filter filters out particles and contaminants. The refrigerant changes to a gas as it warms and is pumped out of the home to the compressor. The compressor increases the pressure and temperature of the refrigerant and pumps it through the condenser coils. The condenser fan helps release the refrigerant’s heat outside. The refrigerant flows through the expansion valve to reduce pressure and cool it further. Once the refrigerant turns back to a cold liquid, it flows back to the evaporator coils to repeat the cycle.

how a central air conditioning unit works illustration
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All of the air conditioner’s components have a role in supplying clean, cold air to your home. The evaporator and condenser coils, the compressor, and the expansion valve are the four main components through which refrigerant flows, transferring heat from the inside to the outside. The fans help to move cold air through the home and release heat outside.


Homeowners must also be familiar with the thermostat and the air filter. The thermostat tells the air conditioner when to cycle on and off, but the homeowner must use the thermostat to turn on the air conditioner and set the desired temperature. The homeowner must change the air filter every 30-90 days for optimal performance.

Air conditioning




A vital fluid coursing through the veins of the AC system, refrigerant undergoes a continuous cycle of compression, condensation, expansion, and evaporation, extracting heat from the cabin air and dissipating it into the atmosphere to uphold a refreshing indoor environment.


Excellent thanks for your topics



This is an interesting article. I had heard that the air conditioner blows cold air instead of removing the heat.

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