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What Is an Evaporator Coil?

What Is an Evaporator Coil?

What Is an Evaporator Coil?

The evaporator coil allows your air conditioning system to absorb heat, which is why an issue such as a frozen evaporator coil is so serious. A dirty coil prevents your AC from blowing cool air (and is one reason why air conditioners freeze up). We’ll explain how the evaporator coil works and why it can freeze. You’ll also receive insights into identifying and addressing common issues, plus advice on maintenance and prevention.

How Does an Evaporator Coil Work?

An evaporator coil is a copper or steel tube located in the air handler or furnace that transports refrigerant. The metal conducts heat efficiently, allowing liquid refrigerant to absorb heat from the air in your home. This turns the coolant into a gas. In the process, the air around the coil cools and is blown into the room or ductwork via a fan. This is how your AC system provides cooling.

The refrigerant (and the heat it absorbs) flows from the evaporator coil to the condenser coil. Fins and a fan around this coil allow heat to be released outside. Both coils work in tandem and form a continuous loop. Heat is constantly absorbed and released while your air conditioner is running.

How Can I Tell the Evaporator Coil Is Working Properly?

If the evaporator coil is working normally, your HVAC system should run as expected. However, if there’s a problem, you may notice signs such as:

  • The AC or heater doesn’t turn on
  • Warm air blows from the supply vents
  • The system starts and stops too quickly
  • Hissing, banging, and other odd noises
  • A sweet or chemical smell, signaling a refrigerant leak

What Causes a Frozen Evaporator Coil?

A frozen coil is not uncommon and can be caused by many issues in your HVAC system. The reasons you might be dealing with a frozen evaporator coil can include:

  • A Buildup of Dirt: Over time, dirt and debris can build up on the coil. This can be due to a dirty filter, but even with proper maintenance, some dirt, dust, and other debris can get through. These interfere with the heat exchange process, so the coil cannot absorb heat efficiently. The refrigerant inside is cold, so condensation on the coil’s surface freezes.
  • Low Refrigerant: A low refrigerant level causes the system to work harder to maintain the desired temperature. There may not be enough coolant to absorb heat energy. This can lead to condensation forming on the coils and freezing. If you have low refrigerant, either it’s been insufficiently charged or there’s a leak, as refrigerant runs in a closed system.
  • A Blocked Duct: A buildup of dust or debris, mold, or a pest infestation can restrict airflow in your ductwork, causing a frozen evaporator coil. A professional duct cleaning can remedy the situation. However, too many closed registers can have a similar effect. They block the return airflow so your AC has less air to work with. Therefore, ensure all floor or ceiling vents are open and not blocked by furniture, cabinets, or rugs.
  • A Clogged Air Filter: When the filter becomes coated in dust, dirt, hair, dander, and other debris, air cannot properly flow through it. The lack of airflow prevents the evaporator coil from absorbing enough heat. A clogged filter can also cause dirt and debris to get inside the system and spread to the coil and other components.
  • Clogged AC Drain Line: Condensation forms on evaporator coils as a normal part of your HVAC system’s operation. The AC drain line helps remove this condensation. But if it’s clogged, excess condensation can form on the coils and freeze.
  • Extreme Cold: Sometimes, a frozen evaporator coil isn’t due to a problem in your HVAC system. Unusually chilly weather can make your home colder than normal. With less heat to absorb, the coils freeze due to condensation on them being exposed to sub-freezing temperatures.

Tips on Fixing a Frozen Evaporator Coil

When your AC isn’t working and you find the coil has frozen up, your first temptation may be to call a professional. Indeed, many issues that lead to frozen coils warrant AC repairs. But depending on the situation, you may be able to resolve the matter. Here are some of your options:

  • Let the Coil Thaw Out: Turn off the system and wait 24 hours for the ice to melt. Or, run it in fan mode, allowing warm air to blow over the coil. Place a bucket or basin under the coil to collect the water.
  • Clean the Evaporator Coil: Coil cleaning can be tricky for a DIYer. But if you’re bold and handy enough, turn off the system at the breaker, locate the coils, and mix warm water and household detergent in a spray bottle. Spray this solution on the coil and wait 10 minutes; use a soft cloth to remove any debris from the surface.
  • Change the Air Filter: A clogged or dirty AC filter can cause a frozen evaporator coil. The air filter should be replaced every one to three months or whenever you notice it’s clogged or dirty. Once you install the new one, let the system thaw and turn it back on. Call a professional if the issue recurs.

How Do I Maintain the Evaporator Coil?

Follow the above tips to prevent the evaporator coil from freezing. Changing the filter as the manufacturer and your local HVAC contractor recommend can avoid this problem. Also, routinely check the coil for any issues, preferably when replacing the filter (as it’s located behind the filter or a panel). 

If the coil is only lightly coated in dirt, go ahead and clean it. However, if it’s extremely dirty, call a professional. They’re trained to use heavy-duty equipment and chemicals to remove debris. For example, they can power wash the coil safely with minimal risk of damage.

Lastly, staying current with regular HVAC maintenance can protect the evaporator coil. Schedule maintenance at least once a year (or once annually for your AC and once for your furnace). A technician will inspect the coil as part of a tune-up and perform any necessary cleaning or repairs.

Have a Frozen Evaporator Coil? Contact Monarch Home Services

Customers throughout the San Joaquin Valley trust us for comprehensive AC maintenance. Our NATE- and EPA-certified technicians are committed to ensuring your HVAC system runs smoothly and efficiently. They clean outdoor and indoor coils, test airflow, lubricate motors, check electrical connections, and perform other tasks to prevent serious problems. Don’t hesitate to call if a frozen evaporator coil occurs frequently. Our team can find the cause and fix it quickly. To request service 24/7 and get a free quote, call (661) 215-6679.

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