What Is a Central Air Conditioner Evaporator Coil?

The evaporator coil is the part of your AC system that actually cools the air before it is blown into your home.

Most homeowners never actually see the evaporator coil because it is covered by a metal case that is usually in an indoor closet or attic. Your evaporator coil is an A-shaped web of copper coils that sits inside your indoor AC unit.

To help you really understand an evaporator coil’s role within the AC system, let’s take a quick look at how your air conditioner works to cool your home.

What most people don’t realize is that AC’s don’t actually create cool air. They simply remove heat from the indoor air, which is where your evaporator coil comes in.

The evaporator coils are filled with very cold refrigerant (a heat transfer fluid). And as warm air from inside your home passes over those cold coils, the refrigerant absorbs all of the heat and moisture from that air. The result? Cold, dehumidified air that gets blown directly into your home.

But what happens to all of the heat that your evaporator coil has just absorbed?

Well, that is what that big metal box in your backyard is for. The refrigerant inside of your evaporator coils carries that heat all the way to your outdoor AC unit. From there, your condenser coils dump all of the heat into the outdoor air.

Your AC repeats that “absorb heat/dump heat” process until your home reaches your set temperature.

During normal, healthy operation, refrigerant is contained within your copper evaporator coils. But over time, those coils can spring small leaks due to normal wear and tear. And when that happens, your AC can’t cool your home as quickly or efficiently as it should.

Signs of a refrigerant leak include:

• Higher-than-normal energy bills
• Ice on refrigerant lines
• Frozen evaporator coil
• Your AC struggles to cool your home
• Hissing or bubbling noises coming from refrigerant lines

Because of the super low temperature of the refrigerant, your evaporator coils need a healthy flow of warm air to prevent them from freezing over. But if they don’t get enough airflow, they will freeze over, limiting your AC’s ability to cool the air. The worst part is that if the problem isn’t fixed, it can eventually destroy your AC’s compressor, which can be a pricey repair.

So what causes low airflow?

• A clogged filter
• Closed vents (even in unused areas of the home)

Over time your evaporator coils can (and will) get dirty. And even a thin layer of dirt can restrict how much the refrigerant can absorb heat from the air. So, dirty evaporator coils can lead to:

• Higher cooling bills
• Less cool air in your home
• Frozen evaporator coils

Do you want to prevent all of the problems listed above? Let’s look at the things you can do to keep your evaporator coils working properly.

We typically recommend checking your air filter at least once a month. And when the filter looks like the one to the right (in the picture below), replace it immediately!

Closing or blocking air vents can restrict the amount of air your AC system can breathe in. And over time, the lack of warm air causes the refrigerant to drop in temperature. Eventually, the lack of warm air causes frost to grow on those cold coils.

Make sure to keep all air vents in your home open, even air vents in unused rooms.

To learn more, check out our blog, “Why Closing Air Vents in Unused Rooms Damages Your Heating/Cooling System”.

Energy Star recommends having annual AC maintenance performed by a professional to keep your system running efficiently.

Regular maintenance protects your evaporator coil specifically because the technician will:

• Replace the air filter if needed
• Clean your evaporator coils
• Check for refrigerant leaks
• Check for (and fix) other evaporator coil issues before they become pricey repairs