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AC Evaporator Coils: Everything You Need to Know

Repairman testing evaporator coil

The ac evaporator coil is an important component to your central air-conditioning system and it plays a vital role in keeping your home cool. When there's a problem with your ac evaporator coil, you'll definitely notice.

If you're not familiar with what a condenser coil is or how it functions within the air conditioning cycle, you've come to the right place. We'll cover everything you need to know about AC evaporator coils and then some. 


 

What is a AC Evaporator Coil

When you think about air conditioning, cold air is probably one of the first things that comes to mind. The cold air delivered actually comes from the evaporator coil. But if you're like most people, you probably think that your AC system is cooling the air, but in reality, heat is being removed. 

It may not sound like much of a difference, but your air conditioner functions in a very complex and complicated way to make this happen. Let's take a closer look:

New ac evaporator coils

As you can see from the above image, the AC evaporator coil is typically upright in an "A" frame shape. The panels are lined with "fins" which are thin metal strips that allow the passing air to get as close as possible to the coil tubing.

The evaporator is where the cold air actually comes from and the coils are made from metals that easily conduct heat. Frequently the coils are made from copper, but steel and aluminum is also used. The tubes are bent into "U" shapes and are stacked into a panel.

There are several steps that take place to cool the air. The image below shows how the ac evaporator coil fits into the refrigeration cycle of a central air conditioning system:

Refrigeration Cycle

The refrigerant travels through an expansion valve before it enters the evaporator coil. The expansion valve plays a very important role, as it reduces the pressure of the refrigerant. During this process the liquid is cooled, which allows it to absorb the heat and thus cool the air.

The blower fan draws hot air from your house over the evaporator coil. As the air passes over, the refrigerant within the copper tubing absorbs the heat.

The compressor keeps the process running by pulling the cold, low pressured refrigerant through the evaporator coils and transfering it to the condenser in a hot, high pressured condition. 

Evaporator Coil Location

The evaporator coil is either attached to the furnace or located inside the air handler. The air handler is the box that houses the blower fan.

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What is a Condenser Coil

The evaporator and condenser coils are both essential to the cooling cycle. Each handles a different side of the process. You might think of it as your favorite basketball team playing offense and defense. Both roles are necessary in order to win a game. 

Where the condenser coil is located plays a big part in the job it performs. You'll find your condenser coil within a large, square box with a big fan on top located next to your house. Since the condenser coil's job is to release the heat from inside your house, it makes sense that the heat would be released into the outside air.

As the refrigerant gas travels from the compressor to the condenser coil. Air is blown over the condenser by a large fan to assist the refrigerant in releasing it's heat.

Within the condenser are many copper coil tubes that wind around the housing. This gives the refrigerant plenty of time to release the heat which was moved from within your home.

Outdoor hose spray
 

Clean AC Evaporator Coils Yourself?

The evaporator coil works when air flows over a series of thin metal fins that are cooled by the refrigerant within the copper tubing. Technically, the evaporator moves the heat from the air into the refrigerant and the cooled air is then blown into the home through the ductwork.

The evaporator coil can be a magnet for dust, debris, and other contaminants, this is because it is installed within the airstream of your HVAC system.

It's critical to have your evaporator coil inspected annually and most DYI'ers are more than capable of cleaning the external surfaces facing the duct airflow.

We highly recommend professional cleaning if you notice an extensive amount of dirt or dust as the surfaces within the coil may also be affected.

 

Pro Tip: Purchasing a quality air filter is the best defense in preventing dirty evaporator coils. And frequent filter changing  is critical. During the cooling season, we recommend changing your filter every 4 to 6 weeks.


The video below will show you how to clean your evaporator coil. You'll need a can of no-rinse coil cleaner which is inexpensive and available through Amazon, and a fin cleaning brush. The job itself is simple but not necessarily easy, especially if the area where the unit resides is not very accessible. 


 

Evaporator Coil Leak

Unfortunately, evaporator coils will leak. There are a variety of factors that can cause leaks, including corrosion as well as a clogged drain. If you find that your evaporator has started leaking, you basically have three options:

Use a Sealant - One option is to inject a sealant into the refrigerant which travels through the system in search of leaks. This method is relatively cost-effective, but may require multiple applications. If the leak is small or moderate sized, there's about a 50% chance that you'll have success.

Add Refrigerant - This option may buy you some time. If your leak is small it may be the most economical choice, especially if you plan on selling your home in the near future. However, keep in mind that your AC system is still leaking and will eventually need to be addressed at some point, and it's possible that there will be long term internal damage.

Replace the Coil - If your evaporator coil leaks, the best and only true fix is to replace the coil. But this is also your most expensive option. It entails opening up the unit and pulling the coil. Refrigerant lines will need to be disconnected, and the system will need to be repressurized. 

Unless you have the knowledge and special tools, these are not DIY repairs. Additionally, many states and even municipalities require licensing for anyone working with refrigerant. That means hiring a professional.

Man counting out 100 dollar bills
 

Evaporator Coil Price

Replacing your evaporator coil isn't cheap. On average, it'll cost about $1,000, but depending on the size and make of your system, it could be as low as $600 or as high as $2,000.

Most manufacturers offer warranties between 5 to 12 years that cover the price of materials, however, you'll still be on the hook for labor expenses, which is typcially 40% of a new installation.

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AC Evaporator Coil is Frozen

A common problem you'll have during the cooling season is a frozen evaporator coil. If you notice your evaporator coil is frozen you need to immediately shut down your system. Failure to do so can damage the compressor.

The evaporator coil's job is to absorb the heat from the air within your house. During normal operation, condensation collects on the coils and evaporates. However, if something isn't working correctly during the cooling process the condensation could freeze.

There are several reasons why your AC evaporator coil is frozen. Let's take a look at the most common:

Inadequate Airflow - This is probably the most common cause and could be the result from a broken air handler or even as simple as closed registers inside the house. Without adequate airflow blowing over the evaporator coil, the condensation on the coil will freeze because there isn't enough heat to be absorbed.

Clogged Air Filter - Air filters are designed to filter out the dust and debris from the air as it passes through your system. However, if your air filter is dirty it'll restrict the airflow which can cause the coil to freeze.

Evaporator Coil Needs Cleaning - If your evaporator coil is dirty it'll make absorbing the heat difficult. The dirt build-up will basically act as insulation keeping the heat away from the coils, which will cause the coils to freeze over because they simply get too cold.

Low Refrigerant - When your system is running low on refrigerant it won't perform as it should. A frozen evaporator coil is a common symptom of this problem.

Improper System Size - An oversized system can deliver too much cooling power for the size of the home; this is extremely common. Because the unit needs a certain amount of airflow, a home that is too small for the AC system can't provide the airflow necessary for it to operate properly. If this is your problem, you'll need to replace the evaporator coil and the outdoor unit. 

All of the above possiblilities can result in an AC system that doesn't perform as designed, and in addition, will shorten the service life of your unit. Regular maintenance and ongoing observation are the keys to proper performance and maximum service life.

Repairman working on air conditioner
 
 
 

How Long Do Evaporator Coils Last?

In theory, there is no reason why your evaporator coil won't last as long as your HVAC system. But this, of course, assumes that you are providing proper care. If you neglect your evaporator coil, you'll most definitely need to replace it at some point.

To get the maximum service life from your evaporator coil you should change the filter monthly during the cooling season. This is by far the least inexpensive and easiest way to extend the service life.

Also, we highly recommend having an annual service conducted by an HVAC professional. The visit will include an inspection of all the major parts, including the evaporator coil and confirmation of proper refrigerant level and pressure.

 

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