What Is an Evaporator Coil?

By Anne Fonda

An evaporator coil, also known as the indoor coil, furnace coil, or “A” coil (because of its shape) is a critical component in air conditioners and heat pumps. In an air conditioning system, its job is to absorb heat and moisture from the air in your home. 

Understanding how a heat pump or air conditioner evaporator coil works and how to maintain it can help you stay cool and comfortable.

An AC evaporator coil is an A-shaped web of tubes filled with cold refrigerant. The coil is paired with your furnace or inside the air handler inside your home. Many evaporator coils are made of copper. However, American Standard coils are all aluminum to reduce leaks that can occur due to corrosives like salt or common household cleaning products.

The blower fan from your indoor unit blows warm air over the coil. The tubes carry a super-cold liquid refrigerant that absorbs heat from the warm air passing over them. As the refrigerant heats up, it turns into a gas. 

Once it has absorbed enough heat to lower the temperature to your desired level set on your thermostat, the refrigerant flows through refrigerant lines connecting your indoor and outdoor units to dump that heat and moisture outdoors. The blower fan then pushes cold air back into your home.

Every cooling system has two HVAC coils - the indoor evaporator coil, and the condenser coil, located in the outdoor condenser unit. While the evaporator coil is responsible for absorbing heat from the air, the condenser coil releases the heat that was taken out of your home. 

The two air conditioning coils work together to cool the air and complete the heat exchange cycle. They form one continuous loop, where the evaporator coils absorb heat and the condenser coils release heat. 

While you may never experience any of these evaporator coil problems, it’s good to know what they are, and how to prevent them.

A clogged HVAC air filter can restrict airflow in your HVAC system, leading to a dirty evaporator coil and potentially a frozen evaporator coil. Prevent a clogged filter by changing your air filters regularly. This should be every 30-90 days depending on the quality of the filter, how hard your system is running, and if you have pets.

A dirty evaporator coil is a common issue and can be a direct result of a dirty filter. The excess dust and dirt collect on the evaporator coil. Dust acts as an insulator and restricts the air circulation that the coil needs to do its job. Prevent a dirty coil by hiring a pro. Professional HVAC maintenance can keep your coil clean.

A refrigerant leak results in low refrigerant which means your cooling system can’t run as efficiently as it should. If you notice an oily residue around your indoor coil or a hissing sound near the indoor coil or outdoor condenser coil, call an HVAC professional right away. You may have a refrigerant leak that should be dealt with by a trained professional. Regular HVAC maintenance can help prevent refrigerant leaks.

If the coil is dirty, the refrigerant running through it won’t be able to warm up as much as it’s supposed to, which causes the water vapor to freeze instead of becoming a liquid. If this keeps happening, the entire coil may freeze and frost over.

Never let your AC unit or heat pump run with a frozen evaporator coil. Because it can’t absorb heat properly, running the cooling system with a frozen coil could cause system failure. Prevent a frozen coil by changing your air filters and scheduling professional HVAC maintenance.

Cleaning evaporator coils is a job best left to a trained HVAC technician. Trying to make it a DIY job could result in damage to your system, a refrigerant leak, or voiding your warranty. By trying to save a few bucks, you could inadvertently cause bigger problems.

The first thing to do is turn your AC unit off and allow the coil to defrost. If you have a heat pump, turn on the defrost mode. Go to your thermostat and switch it from Cool to Off. 

You can speed the thawing process by turning the HVAC system fan to On at your thermostat instead of Auto. The blowing fan at the furnace or air handler will help thaw out the evaporator coil.

While the evaporator coil is thawing, call for emergency AC repair if you’re in the middle of a Texas heat wave. If it’s evening and the temperatures are moderating, you may be able to schedule in a day or two. Just don’t turn the system back on until the coil has defrosted and you’ve changed the filter.

With regular professional HVAC maintenance, the indoor coil can last 10-20 years. A high-quality coil like those from American Standard can last longer.

Failure to have the evaporator coil regularly cleaned and inspected can shorten the expected lifespan. The coil also may not last as long if you run your air conditioner continually throughout the year.

If your evaporator coil fails, you’ll have two choices: replace it or replace the entire indoor unit. Evaporator coil replacement cost isn’t cheap, and between parts and labor can run into thousands of dollars.

Talk with your HVAC professional about your options and what the most cost-effective solution is. If you choose to replace an evaporator coil, the refrigerant must be compatible with the refrigerant your condenser unit uses. You can also refer to our Repair or Replace Guide for more information. 

To keep your evaporator coil and other HVAC system components in top condition, you need to schedule regular HVAC maintenance. Your HVAC technician should visit in the spring and the fall, before the cooling and heating seasons begin. They will inspect, clean, and test your air conditioner, heat pump, or furnace, depending on the season and the equipment you have. Contact your local American Standard HVAC expert to schedule now.

A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need. 

She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism. When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.

Expert review by Sean Goddard, Product Manager, Coils & Indoor Air Quality