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Top 5 Causes of Frozen AC Coils


Unlike other HVAC malfunctions, frozen AC coils can be caused by failures in almost any part of the system. If you see frost or a layer of ice on your indoor unit, that’s obviously a problem… but it’s not so easy to diagnose the reason.

In this article, we’ll explain the possible causes of frozen air conditioner coils, and what to do next if it’s happened to you.

Symptoms of frozen AC coils

With frozen coils, there’s going to be ice or frost on the coils and possibly pipes of your indoor unit. However, many indoor units aren’t accessible, so you might not be able to see that. So what are some other symptoms of frozen air conditioner coils?

  • The first symptom of any HVAC problem you are likely to notice is the heat. If your AC doesn’t feel like it’s working as it should, there are a few things you can inspect to get more info on the problem.
  • Check the air flowing through the supply registers. If it’s warm or the air is stopped altogether, frozen coils could be the problem.
  • Frozen AC coils can lead to a buildup of moisture, which could cause condensation or water leaks in your building.

Read on to learn about the top 5 issues that can cause your AC coils to freeze.

Why does your system have frozen AC coils?

1. Dirty air filters can cause frozen AC coils

Your AC needs clear air flow throughout in order to function properly. Dirty filters can obstruct the air from getting in and out.

If air is not circulating around the coils, the coils get too cold, leading to accumulating ice.

2. Broken fans can impede air flow and cause coils to freeze

Even if your filters are clean, it won’t help unless the fan is pushing air through the system.

If your fan has a broken motor, or even just dirty blades, this can cause a lack of air flow that could lead to frozen AC coils.

3. Frozen AC coils are caused by blocked condensate lines

Condensate lines are the part of your HVAC system that drains away excess moisture from humidity. This moisture, condensed into water, travels through pipes to a floor drain.

If the water is stuck in one place because of a clogged pipe, it can freeze. This is especially true if the obstruction happens near the evaporator coil, the coldest part of the AC. A blocked condensate line can cause the water, and subsequently the coils to freeze.

4. Malfunctioning thermostats lead to frozen air conditioner coils

Your thermostat works with your AC by regularly checking the temperature and controlling how hard the AC has to work to keep the building a consistent temperature.

If a broken thermostat senses the wrong temperature, or controls the AC improperly, it could cause the unit to run too long and wear out the system. You might suspect this if you have trouble keeping your building at a steady temperature, or if it frequently runs too cold.

Left unchecked, an overworked AC unit could develop frozen AC coils.

5. Refrigerant leaks are a common cause of frozen coils

Refrigerant is the chemical that runs through your AC coil, changing pressure and temperature in order to absorb heat. If it leaks, the lack of pressure will make it absorb more heat than it should. This makes the refrigerant lines, and then the coils, freeze over.

Not only is leaking refrigerant bad for the environment, in some places it is illegal to leave refrigerant lines leaking. That’s why a professional should fix the leak or replace the coil rather than just filling it up with more refrigerant.

What to do if you have frozen AC coils

Ok, so you’ve determined that your air conditioning coil is frozen. You might even be able to tell which of the five causes resulted in your problem. So what should you do next?

First of all, SHUT THE UNIT OFF. This is vitally important to prevent compressor failure.

Related topic: 8 Ways to Avoid AC Compressor Failure

Because of the potential for system damage, it’s in your best interest to call a professional. They will also be able to get to the bottom of the cause and get your unit back up and running fast.

There are a few things you can do yourself while waiting for further help.

  • Find and clean up any water damage. If your frozen AC coils caused water leaks from melting ice, it’s a good idea to clean them up and prevent damage to your building.
  • Try to melt the ice. You should turn your system off and wait for the ice to melt, or possibly use a hair dryer to melt it. Never try to cut or chip the ice off, because you risk damaging the coils.

How a preventative maintenance plan will keep frozen AC coils from happening to you

Does all this sound like more than you want to worry about? You may not have to. The easiest way to avoid AC problems is to get a preventative maintenance plan.

Preventative maintenance plans include an inspection and upkeep for your AC from an HVAC specialist. These system checks are most useful before you begin use of your AC in the summer and after you turn it off for the season in fall. The specialist will take care of maintenance tasks such as changing filters, cleaning the coils, and inspecting the lines for leaks.

Frozen AC coils are usually the result of a smaller problem that’s been left unchecked for too long. A preventative maintenance plan would ensure that you notice a problem right away, and have it taken care of before it causes your air conditioning to fail or creates a more costly problem.

Related topic: 8 Ways AC Preventative Maintenance Keeps the Repairman Away

Taking care of your HVAC unit over time with a preventative maintenance plan is more cost effective than dropping more money on big repairs. It also makes sure you never lose a day’s worth of business or have work halted by an AC failure. That means you can relax and get on to more important things.

Learn more about how to get the right HVAC maintenance plan for your needs with this helpful guide to HVAC Preventive Maintenance Contracts: How to Find The Right One For Your HVAC Infrastructure.

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