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What Is an Evaporator Coil?

Evaporator coil definition, how it works, how to keep it clean, and what it costs to replace

Chances are, you’re not interested in a dysfunctional air conditioner or heat pump that never turns on when it’s hot outside. And you’re probably really not interested in a cooling unit that blows out warm air in the middle of a hot summer day. That’s why it’s important you (with the help of a professional HVAC technician) keep your HVAC system’s evaporator coil in the best possible shape.

Your evaporator coil is a major part of your heat pump or AC unit because it absorbs heat from inside your home. It then works with other parts of your air conditioner to cool your home by transferring all that heat outside. And of course, with a heat pump, the evaporator coil gets a workout in the winter as well as the heat pump reverses the flow of refrigerant to heat your home.

That means if your evaporator coil is broken, your home won’t get as cool as you want it. Understanding how an evaporator coil works and what you can do to maintain it will play a big role in saving you the heartache of a broken air conditioner in the summer.

By Anne Fonda  

So, what is an evaporator coil, exactly?

An evaporator coil is the component of your heat pump or air conditioner that absorbs the heat and moisture from the air inside your house. It works alongside the condenser coil to produce cool air and complete the heat exchange cycle. The evaporator coil is also sometimes referred to as the “A coil” because of its shape.

Warning: Your air conditioner is a dangerous, high-voltage device. Touching or mishandling the internal components could lead to serious injury or death. Always consult an experienced and licensed HVAC technician if you’re experiencing problems with your air conditioner.

How does it work?

To understand how an AC evaporator coil works, it’s important to understand how an air conditioning unit functions as a whole. Unlike how a furnace produces heat, an air conditioner doesn’t actually produce cold air. Instead, the system removes heat from the air in your home, carries the heat through the air conditioner, and sends that warm air outside. 

To do this, refrigerant flows throughout the entire air conditioning system, carrying and releasing heat, to ultimately cool the air. This cycle repeats itself continuously until enough heat has been taken out of the air in your home so that the air temperature matches the temperature set on your thermostat.

Evaporator coils are typically made of copper or rust-resistant aluminum — two metals that conduct heat well. As your house’s air passes through the evaporator coil, the coil absorbs heat and water from the air. The heat is transferred to the refrigerant by boiling the refrigerant (evaporating) and is carried outside to the condenser coil. 

Water is condensed when the warm house air passes through the cold evaporator coil. This condensation is drained through a separate pipe and drained outside.  The condenser coil then transfers the heat from the refrigerant to the outside air by condensing the refrigerant back into a liquid. 

As more and more heat is absorbed and released, cool, refreshing air is dispersed throughout your home. Most AC evaporator coils should last between 10 and 15 years, as long as maintenance is regularly performed.

Where is the evaporator coil located?

In a ducted system, the evaporator coil is generally located inside your home and attached to your furnace or housed inside your air handler, depending on the system. Only a trained HVAC professional should access the evaporator coil.

What’s the difference between an evaporator coil and a condenser coil?

Although the evaporator coil and condenser coil work together to cool your home, the two perform very different tasks. While the evaporator coil is responsible for absorbing heat from the air in your home, the condenser coil is where the captured heat is released to the air outside, How do these two work together?

Evaporator coils and condenser coils work in tandem to produce conditioned air and complete the heat exchange cycle. They form one continuous loop, where the evaporator coils absorb heat and the condenser coils release heat. The air conditioning process could not be completed without both sets of coils. In a heat pump system during heat mode, the refrigerant cycle reverses and heat is absorbed from the outdoor air and released to the indoor air inside your home.

More on A/C condenser coils

The condenser coil is located inside of the AC or heat pump unit outside your home. During the refrigeration cycle, the condenser turns the refrigerant into a hot, highly pressurized gas. This gas then flows through the condenser coil, which releases the heat to the outdoor air.

How do you know if your evaporator coil is bad?

Some telltale signs let you know when you should hire an HVAC technician to inspect your evaporator coil. You may have a bad AC evaporator coil if your unit is:

  • Not turning on.
  • Releasing warm air from the vents inside your house.
  • Starting and stopping without completing cooling.
  • Making strange noises like a hiss or bang, coming from inside or outside the unit.
  • Producing a refrigerant leak that you can see near the indoor cooling component.

WARNING: AC refrigerant is a toxic chemical. Touching or mishandling AC refrigerant could lead to serious injury or death. Keep small children and pets away from any refrigerant leaks. Always consult an experienced and licensed HVAC technician if you’re experiencing problems with your air conditioner or heat pump.

If you identify any of these issues with your unit, you may need to contact an HVAC professional to clean or replace your evaporator coil.

Top evaporator coil issues

A licensed HVAC professional can inspect your evaporator coil to diagnose the following issues. Do not attempt to inspect or maintain your evaporator coils yourself.

Dust build-up

It’s extremely important to change your air filter every 1-3 months, based on your filter type. If you don’t, your evaporator coil may be in jeopardy. When the air filter becomes clogged, excess dust and dirt begin to deposit onto the evaporator coil, causing it to run less efficiently. Dust on an evaporator coil acts as an insulator, keeping the heat in and the air away from the coils. This means your system will have to run longer, use more energy, and potentially face more issues in the future.

Frosting over

Another issue that could arise from a dirty evaporator coil is the entire piece frosting over. 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 air conditioning unit run with a frozen evaporator coil, because it won’t be able to absorb heat correctly, and could result in the entire AC unit breaking.

Leaks

Because the evaporator coil is where heat is absorbed, tiny leaks can form from the mixture of condensation and the chemicals found in household air. If you start seeing oily residue on or around your evaporator coil that’s likely a sign it’s leaking and needs to be serviced by a licensed HVAC professional soon.

Why a clean evaporator coil is a good thing

If your AC evaporator coil is dirty, but still functioning, don’t push it off to address later. A dirty, yet still functional, evaporator coil takes a longer time to cool your home and causes poorer indoor air quality overall.

Lastly, having your evaporator coil serviced regularly keeps your home at the temperature you desire. A dirty evaporator coil could mean living in a higher-temperature environment. Contact a licensed HVAC technician to keep your heat pump or AC unit in optimal condition.

How to clean an evaporator coil

You should not attempt to clean an evaporator coil yourself. Doing so could void your warranty or damage the coil. 

Your air conditioner is a dangerous, high-voltage device. Touching or mishandling the internal components could lead to serious injury or death. Always consult an experienced and licensed HVAC technician if you’re experiencing problems with your air conditioner.

It’s best to have your evaporator coils cleaned and maintained by a licensed HVAC technician at the same time you’re having your entire cooling system cleaned and maintained. Make sure you change your air filters regularly, an HVAC professional inspects and maintains the refrigerant levels in your unit, and always report any issues you may see, hear, or feel coming from your HVAC system.

Scheduling regular HVAC maintenance is critical. Always get help from a professional to clean and maintain the inner workings of your unit, including evaporator coils. HVAC professionals are trained and have the proper equipment to safely keep your HVAC system and components clean and debris-free.

How low refrigerant can affect evaporator coil performance

Refrigerant is the lifeblood that flows throughout your entire air conditioning or heat pump system. When refrigerant is low, your entire unit may fail to function as it should. Refrigerant levels should remain constant as the cycle is in a closed loop.

If your refrigerant levels are low, it means you have a leak somewhere, or the system was improperly installed. Contact an HVAC professional if you suspect you have a refrigerant leak. 

Can this be repaired?

If the evaporator coil is leaking or frosted over, it may need to be replaced. If the evaporator coil is simply dirty, an HVAC professional may be able to use cleaning techniques to repair the coil without replacing it.

Evaporator coil replacement

Always consult an experienced and licensed HVAC technician if you’re experiencing problems with your air conditioner. If they determine that your evaporator coil needs to be replaced, they will first give you an estimate. You’ll have to decide if coil replacement or replacing an older HVAC system makes more sense. Consult our Repair or Replace Guide for guidance.

How much does it cost to replace an evaporator coil?

Not having to replace your coil can be a good thing for your bank account! Evaporator coil replacement costs can range anywhere from $550-$2,500, depending on whether your unit’s under warranty or not, the size of the AC coil, and more, according to Forbes. If an HVAC technician can repair an evaporator coil without fully replacing it, your wallet is in luck.

Additional guidance

Why you can trust us

When we compile information like this, our goal is to help homeowners like you make informed decisions. We work with HVAC engineers and HVAC professionals with decades of experience. Our glossary items and blogs undergo expert review to ensure you get the accurate and up-to-date information you need.


Anne Fonda, Content Writer at Trane Technologies

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, Evaporator Coils, and Leslie Zinger, Lead Product Development Engineer, Engineering

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