How Does Central Air Conditioning Work?

June 20, 2021
Central Air Conditioning in Seattle, Washington

The primary purpose of a central air conditioner is to draw warm air from the house and blow in cool air in the hot summer months. It also draws out excess moisture and filters contaminants to create comfortable indoor conditions.

If you own a central air conditioning unit, it’s essential that you familiarize yourself with how it functions. That way, you’ll know the AC system’s main components, and you can easily spot when they malfunction and seek immediate help before the issue escalates into a bigger problem. Here are the steps involved in the air conditioning process.

1. The Thermostat Signals the AC to Kick On

The thermostat is the controller of the AC unit. It mainly reads the house temperature and prompts the air conditioner to turn on or off. When the indoor temperature rises beyond the set range, the thermostat sends a signal to the AC unit’s control board to start running, and the cooling process begins.

If you have a programmable thermostat, you can set it to adapt to your schedule so that it cools the house only when you’re home to conserve energy and save money. Note that if a thermostat malfunctions, it can affect the cooling process. You should check your thermostat’s accuracy before the beginning of the cooling season.

2. The Blower Motor Draws Out Warm Air

The air handler pulls in warm indoor air via the blower. This component is also responsible for blowing back cooled air into the house. The warm indoor air then proceeds to the evaporator coils.

When the blower fan malfunctions, it might not draw warm air out efficiently or blow in enough cool air. You should clean it often to prevent the accumulation of dirt on the blades.

3. The Air Goes Over to the Evaporator Coils

The evaporator contains some aluminum fins, and it’s responsible for extracting heat from the indoor air. It also has a refrigerant, a special fluid that changes state from liquid to vapor and back in favorable temperatures to aid in heat exchange. When your indoor air flows over the cold evaporator coils, the coolant absorbs latent heat from the air. It then transforms from a liquid into a vapor.

This process works under the principle that heat flows from hot to cold regions naturally. The indoor air will lose warmth and humidity. When the moisture hits the cold evaporator coils, it condenses and forms a liquid. The water then flows to the condensate pan, which drains to the outdoors. Once the air cools, it flows back into your house via ductwork. These are a series of hollow tubes that carry the conditioned air to various rooms in your residence.

The air will also pass through a filter, which collects dirt, dust particles, pet dander, and other contaminants. There are supply vents in every room that help recirculate the cool air. The warm refrigerant vapor then flows to the compressor. Evaporator coils require professional cleaning before the beginning of the summer season to protect them from debris accumulation.

4. The Compressor Pressurizes the Refrigerant

The refrigerant in the gaseous form must pass through the compressor to prepare it to expel the heat drawn from the indoor air. This component is at the heart of the air conditioner in the outdoor unit. The compressor mainly squeezes the vapor refrigerant tightly together to increase its temperature and pressure. This process follows Boyle’s, Gay-Lussac’s, and Charles’ laws that state that an increase in pressure increases the temperature.

The main reason behind heating the refrigerant is to get it to a temperature beyond the outdoors. Keep in mind that the coolant needs to be hotter than the outdoor air to facilitate natural heat flow. The high-pressure, high-temperature refrigerant then flows into the condenser coils.

Note that refrigerant leaks can lead to compressor damage, so you should have a technician check your unit often for leaks. There are limited chances of compressor repair, and if it malfunctions, you might need to replace it or even the entire system.

5. Heat Transfer in the Condenser

The condenser coil is in the outdoor air conditioning unit, and its primary role is to help dissipate the heat drawn from the indoor air outside. A condenser coil operates the same way as the evaporator coil, but it releases heat to the outside rather than absorbing it. This component contains a condenser fan that facilitates heat transfer.

The condenser fan draws in cold air and blows it over the condenser coil, and heat begins to flow from the refrigerant to the outdoors. As the heat moves from the coolant, it changes state from a gas to a liquid, and then it flows into the expansion valve.

Since the condenser is an outdoor component, it’s more prone to accumulating debris and dirt. Clear off any plants growing next to the outdoor unit, and clean the condenser often to allow for efficient operation.

6. The Refrigerant Flows to the Expansion Valve

Once the refrigerant releases all the heat, it flows to the expansion valve. The refrigerant needs to cool down before it gets to the evaporator coils. Hot coolant won’t absorb the latent heat as the warm indoor air flows over the coils. The expansion valve depressurizes the heated liquid refrigerant. Following the combined gas law that a decrease in pressure results in a drop in temperature, the refrigerant cools.

A reduction in pressure causes the refrigerant to expand, which throws off a lot of energy, rapidly cooling the refrigerant. The coolant then flows back to the evaporator coil. The expansion valve also controls the amount of refrigerant entering the evaporator coil based on the temperature in the suction line.

7. The Cooling Cycle Repeats

The low-pressure liquid refrigerant from the expansion valve flows through the refrigerant line into the evaporator coil. From here, the cooling process will continue over and over again until your house achieves the desired temperature. On scorching days, your AC unit might run continually for a more extended period. Once your home attains the set temperature, the thermostat will signal the air conditioner to stop running until the temperature rises again.

Are You Having Trouble With Your AC Unit?

An air conditioner is the most convenient way to get relief from the humid summer weather. You need to schedule regular maintenance for your central AC unit to keep it running at peak efficiency. There are some simple maintenance tasks that you can do on your own, like changing the air filters, cleaning the condensate pan, and clearing away debris around your unit. You should, however, leave complex tasks like recharging the refrigerant, cleaning the coils, fixing loose electrical connections, and lubricating motors to a professional. Besides ensuring that your air conditioning system runs smoothly, preventive maintenance reduces energy bills, prevents frustrating breakdowns, and extends the unit’s lifespan. Maintenance also keeps your equipment under warranty, saving you a substantial amount of money should anything go wrong with your AC unit.

If your air conditioner isn’t working as expected, reach out to Brennan Heating & Air Conditioning. We specialize in cooling and heating installation, maintenance, and repair. We also offer duct cleaning, heat pump installation, free energy consultations, and water heater installation services across Seattle, WA, and the surrounding areas. Contact us today to schedule an appointment.

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