What causes a frozen evaporator coil and what can you do about it?

It’s the hottest day of the year, and your air conditioner just stopped working. You walk outside to inspect the outdoor unit and you’re greeted by a strange sight: ice. As it turns out, you have a frozen evaporator coil. In this article, we’re going to talk more about what causes this phenomenon and what you should do if this happens to your air conditioning unit.

At King Heating, Cooling & Plumbing, we’re here for you and your home’s air conditioning needs with our 24/7 emergency service. Call us today for fast, reliable air conditioning repair.

Preventing a frozen evaporator coil here in Chicago.

Schedule an AC tune-up with King every spring and have one of our technicians look at your refrigerant levels ahead of summer.

What causes an evaporator coil to freeze?

Let’s start by talking about how your air conditioner works in the first place. In the simplest of terms, air conditioners (and heat pumps, in their summer setting) are able to cool down your home by moving heat energy from one place to another. The evaporator coil contains refrigerant that runs inside and outside in a constant, contained loop. As the refrigerant enters the inside portion of its circuit, the molecules expand, cooling down the line and allowing it to absorb heat energy from the air in your home.

It then returns to the outdoors, where the condenser condenses those same molecules, causing the line to heat and expel that heat energy into the outdoor air. This happens over-and-over again until sufficient heat energy is removed from your home to bring it down to the temperature where things are comfortable.

In the event that heat energy is not able to be absorbed into the refrigerant, things start to go wrong. Most often, this occurs because the return air—the heat energy-filled air inside of your home—is unable to get to the line. As a result, the refrigerant in the line begins to get colder with no heat to absorb. The line gets cold enough that the condensation on the outside of the line—which normally drains away harmlessly—freezes over, leading to a literal block of ice.

What are the most-common causes of this problem?

Essentially, anything that blocks airflow to the evaporator coil can lead to a frozen evaporator coil. Here are some of the most likely culprits:

Dirty coil

Over time, your system’s evaporator coil will become covered in dust, dirt, grime, and more. This prevents it from getting the airflow it needs to properly move heat, which means that the system could then freeze over. Evaporator coil cleaning is an essential part of our AC tune-up service for this exact reason.

Blocked air ducts

In the event that you’ve manually shut many of your home’s floor or ceiling registers, the return air flow to the coil may not be getting sufficient airflow to continue operating correctly. Another common cause of this problem is when homeowners unknowingly block floor registers below furniture or rugs. Similarly, an extremely dirty air filter can block a main source of air from reaching the line.

Low refrigerant

The refrigerant line is a closed-loop system. However, in some cases, refrigerant may be lost through leaks or other problems. Without enough refrigerant, the molecules expand too much, causing a runaway cooling effect that results in a frozen-over system.

How should you go about fixing this problem?

First things first, you’re going to want to turn off your air conditioner. At this point, any further operation by the air conditioner is just going to keep refreezing the already-frozen line. Then, call the trusted technicians here at King Heating, Cooling & Plumbing. We offer 24/7 emergency AC repair services throughout Chicagoland. When our tech arrives at your home, they’ll inspect the problem and then likely switch the thermostat to its fan-only setting to accelerate the thaw.

Once the system has fully thawed out, we’ll need to address the original cause of the problem. It’s likely one of the three culprits listed above: dirty coils, blocked air ducts, or low refrigerant. If it the latter, we can recharge the system with the appropriate refrigerant type and address any leaks that caused the system to lose refrigerant in the first place.

Call King for 24/7 emergency AC repair

At King, we’re your 24/7 AC repair experts in Chicago, Oak Forest, Homewood, Frankfort, Chicago Heights, Joliet, and surrounding areas. If your air conditioner has a frozen evaporator coil or any other problems that are preventing it from operating properly, call us today. We’re ready to help!

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