What Are Evaporator and Condenser Coils and How Do They Help Cool Your Home?

Posted on: April 17, 2015

Given the Raleigh/Wake Forest area’s hot summers, you probably know some basic facts about your air conditioner, but do you know how the evaporator and condenser coils actually operate? If the inner workings of your A/C are a mystery to you, you’ll benefit from learning a few simple technical details about how your cooling system does its job.

shutterstock_243671491-200x300No matter how much your air conditioner operates, it’s important to perform routine A/C maintenance that keeps your evaporator and condenser coils and the rest of your system running efficiently. If something does go wrong, you’ll be better able to troubleshoot the problem. Your knowledge will also help you make smart choices when you’re ready to buy replacement components or upgrade your air conditioner.

 

Get to Know the Evaporator Coil

Air conditioners don’t actually “produce” cold air in the way a furnace produces heat. Instead, they use refrigerant, or coolant, to absorb heat from the air, carry that heat outdoors, and release it into the air outdoors. The refrigerant circulates continuously to remove more and more heat from your home until your indoor air temperature reaches the one you’ve chosen on the thermostat.

Evaporator and condenser coils handle different sides of the cooling cycle. An air conditioner‘s evaporator coil, also called the evaporator core, is the part of the system where the refrigerant absorbs heat. That is, it’s where the cold air comes from.

The evaporator coil is located inside or near the air handler where the blower fan is. Evaporator coils are made from copper, steel or aluminum because these metals conduct heat easily. Most residential A/C evaporators consists of tubes bent into U-shapes and set into panels.

The panels are typically positioned in the form of an A. These panels are lined with thin pieces of metal known as “fins,” which bring the passing air to be cooled closer to the coils in order to maximize the effect of the refrigerant.

As the air conditioner runs, the compressor pulls cold, low-pressure liquid refrigerant through the tubing in the evaporator coil. Before entering the evaporator coil, the refrigerant passes through the expansion valve. This valve relieves pressure from the liquid refrigerant, which rapidly cools it. The liquid refrigerant leaving the expansion valve is quite cold, which is what allows it to absorb heat from the air.

The expansion valve also controls exactly how much refrigerant flows to the evaporator. More advanced expansion valves, such as thermostatic expansion valves (TXVs), can minutely control the flow to improve the system’s overall energy efficiency.

As the refrigerant flows, the blower fan draws hot room air over the evaporator coil. The refrigerant absorbs heat from the passing air and, as it does so, it warms up and evaporates.

When the water vapor in your warm household air hits the cold evaporator coils, the water vapor condenses into liquid form and drips down into the condensate pan, which drains the water away outdoors. This is how your evaporator coil reduces the humidity in your home.

Caring for the Evaporator Coil

Because of the way they operate, evaporator and condenser coils both need to be kept clean to perform as intended and reach optimal energy efficiency. A dirty evaporator coil can experience a number of problems, including:

  • Impaired heat absorption and cooling capacity
  • Higher energy use
  • Higher pressures and temperatures
  • Frost and ice buildup

Even a fine layer of dust on the evaporator coil reduces its efficiency. The dust acts as an insulator, keeping the heat in and the air away from the cold coils. That means the coil can’t absorb as much heat as it can when clean. Your system will then have to run longer to provide the indoor temperature you want, which means it will use more energy.

Because it isn’t absorbing enough heat, the refrigerant running through a dirty evaporator coil doesn’t warm up as much as it should. This very cold refrigerant causes water vapor in your air to freeze rather than condense into a liquid. Eventually, the whole evaporator coil can frost over.

A layer of frost on your evaporator is never normal. Letting your system run with a frozen evaporator raises the temperature in the compressor and can eventually cause this component to fail. Dust on the evaporator coil, debris on the outdoor condenser unit, a dirty air filter, and a refrigerator leak can all cause the evaporator to freeze. If you can’t pinpoint the problem, contact a heating and cooling technician.

Evaporator coils can also develop tiny pinhole leaks due to corrosion caused by the mixing of moisture from condensation with chemicals commonly found in household air. Oily residue around the evaporator or in the drain pan is a sign your coil is leaky and requires replacement.

The airborne chemicals that encourage these leaks are known as volatile organic compounds (VOCs) and come from new carpeting, upholstery, pressed wood furniture, air fresheners, cleaning chemicals and many other sources. Ensuring good home ventilation reduces the VOCs in your indoor air, protecting both the evaporator coil and your health.

How the Condenser Coil Does Its Job

Evaporator and condenser coils work together to cool your home, so the evaporator coil wouldn’t be much good without a condenser coil to complete the second half of the cooling cycle.

Your air conditioner’s condenser is contained in the large, square unit outside your house. Although the whole unit is called the “condenser unit,” it actually contains multiple components, including the condenser tubes and fins, the compressor, a fan and copper tubing, as well as valves and switches.

After the refrigerant absorbs heat from your home’s air, it travels outside via a copper tube to the condenser unit. Here, the low-pressure, warm refrigerant gas enters the compressor. The compressor pressurizes the refrigerant, turning it into a hot, high-pressure gas.

This gas leaves the compressor and flows into the condenser coils. This is where the refrigerant releases much of the heat it absorbed from your home. The fan on top of the outdoor unit blows air over the condenser coils so the refrigerant inside loses heat. The condenser’s many coils increase the amount of time the refrigerant is in the path of blowing air, giving it plenty of time to release the heat it carried out of your home.

As it cools, the refrigerant changes from a hot gas to a hot liquid. From there, it flows back through a copper tube into your home and into the expansion valve located in the indoor unit near the evaporator coil.

Keeping the Condenser in Shape

Good airflow is critical for both evaporator and condenser coils. Both these components transfer heat, and dust or debris interferes with their ability to do this. For condenser units, the most common threat is a buildup of yard debris on the fins. This usually takes the form of grass clippings, fallen leaves, twigs and pet hair that make it harder for the condenser to release heat. This reduces your A/C’s energy efficiency and places strain on the condenser and other components.

Check the condenser periodically and, if you notice debris buildup, shut off power to your whole system and use a stiff brush to gently clean the fins.

On occasion, an air conditioner condenser can develop frost or even a complete casing of ice. Assuming the condenser unit itself is clean, ice-ups like this usually mean there’s an airflow problem elsewhere in your system. This could be a dirty air filter, dirty air registers and vents, a duct blockage or a dirty evaporator coil. Ice on the condenser can also be caused by low refrigerant, which requires a call to a technician.

When the cooling season ends, protect the outdoor condenser from the elements by covering the top with a piece of wood held down at all four corners by bricks. This keeps snow from piling up inside.

You may have seen your neighbors’ condensers wrapped up in plastic for the winter, but this approach can do more harm than good. Covering the whole unit traps moisture inside, encouraging rust. It also makes the unit more tempting for animals seeking shelter.

Learn more about evaporator and condenser coils, as well as our air conditioning solutions, or call 919-887-2132 to schedule an appointment!

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