Why Is My AC Freezing Up? How to Fix it? [With Pictures]

It happens all over America. And the rest of the world probably. It’s the hottest day ever and for some darn reason your AC isn’t cooling the house. You fiddle with the thermostat to try and fix the problem. Nada. All you can do now is go outside and check the AC unit. You make your way there and find your air conditioner unit is frozen! But how?

In this post we’ll cover how you can tell that your air conditioner has frozen (other than the obvious reasons), what could have caused the freeze, and some of the things you can do about your AC freezing up. And if you have a frozen heat pump condenser, read our blog about it to learn what to do! But remember, it is always best to avoid your AC freezing up with an AC tune up. And if you are moving into a home, it's critical to get HVAC inspection so that you are aware of an AC problems before you move in.

Keep reading and you may be able to fix the frozen AC yourself. If you can’t, call an HVAC specialist. If you live in Maryland, call SuperTech HVAC for AC repair. We’ll take care of it. 

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Frozen Evaporator Coil

Bring the chill Factor Back ASAP

How Does An Air Conditioning Unit Work?

How you probably imagine an AC works is wrong. Contrary to popular belief, an AC system does not inject cool air into a building. Instead, it removes the heat from inside and transfers it outside. Cool huh? (Pun intended).There are 4 major components among the 3 stations of an air conditioning system: the evaporator coil, the compressor, the condenser, and the refrigerant – a special chemical that links everything together through a closed loop system.

Station 1:

Warm indoor air is sucked into the return vent, through a filter, and blows over the evaporator coil. The heat is absorbed into the cold refrigerant, turning it from liquid to gas. The air, which is now cool, is blown back into the home to areas that your thermostat, i.e. you, has decided.

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How AC cools air

Station 2:

The refrigerant makes its way outside the house to the compressor, which squeezes the warm refrigerant, raising its gaseous temperature even more.

Station 3:

When the super hot vapor refrigerant reaches the condenser, the last step, the heat is expelled and absorbed into the outdoor air. The refrigerant instantly cools, which changes it from gas back to liquid form. The cold liquid refrigerant is now ready to return to station 1 and repeat the process.

Go science.

Is Your AC Freezing Up? Here Are The Signs:

As you may have guessed, your air conditioner unit freezing up on a hot day is not normal.

If this happens, there's no need to panic. Often the issue can be solved with a little troubleshooting. If the AC unit is left frozen for too long however, you may find yourself with a bigger problem.

First things first, how do you know your AC is frozen?

Well, the obvious sign is the ice on your refrigerant line-set pipe. Simply check between your outdoor AC unit and your home's exterior wall to see whether your AC line frozen.

You might also have a frozen evaporator coil. This one's not as easy to check. You'll need to open a panel on the indoor unit to inspect. Don't do this unless you're handy. If you aren't, call an HVAC pro like SuperTech HVAC or you may damage something in the process.

Seeing frozen AC parts isn't the only way to tell your AC frozen.

There are some other, less obvious signs your AC is frozen:

  • Your AC is not sending cool air back into your house.
  • Condensation has formed on the surface of the indoor unit.
  • Condensation has formed on the exterior of the condensate drain.
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Frozen Line-set

Why Is My Air Conditioner Freezing Up?

The answer is simple: there is little to no air flow.

If there isn’t enough warm air blowing through the evaporator coil to transfer the heat, the refrigerant will not turn to warm gas. Instead, the refrigerant freezes – in the evaporator coil or in the line.

No bueno.

Poor air flow is the singular root of the problem, but there are many reasons why that might happen.

Here are the most common things that lead to compromised airflow, which leads to your air conditioner freezing:

Clogged Air Filters

An accumulation of dirt on the filter blocks the flow of warm indoor air. The next thing you know, you have a frozen AC unit. So make sure you replace your filters often, and read our how-to guide if you don't know how.

Blocked or closed supply and return vents – furniture or even curtains blocking return vents or closed supply registers to save energy; These missteps block air flow, which could easily leave your air conditioner frozen. Be careful. 

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Clogged AC Filter

Clogged Condensate Lines 

Moisture from the air is absorbed through the evaporator coil along with heat. A drainage line leads the condensed moisture (water) away from the cold refrigerant in your AC unit. If the drain line is blocked, water becomes trapped near the evaporator coil and freezes. 

Damaged Blower Fan

This pushes warm air to the coils. If the AC blower fan is malfunctioning and not blowing any air, or not blowing enough air, then eventually the frozen evaporator coil will stop the air conditioner from working.

There are a lot of reasons that can cause one or more AC fan breakdown, which we talk about it our blog about broken fans.

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Broken Blower

Dirty Coil

If dirt cakes the evaporator coil, the airflow will become restricted and it will freeze. When your home's indoor air travels in your ducts, it carries dust. Your filter helps capture most of it, but not all of it. Over time, the coil will get dirty and need cleaning. If not, bio-growth may develop on it and cause your AC air to smell musty when flowing into your house.

This is why it's important to have regular maintenance checks by a professional.

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Dirty/Moldy Evaporator Coil

Low Refrigerant Level

The higher the pressure, the hotter the refrigerant (this is what happens in the compressor). When there’s a refrigerant leak, there is less refrigerant. When there’s low refrigerant, it becomes less pressurized, which leaves your AC line frozen.

If you'd like to know more, read our blog about refrigerant leaks.

Collapsed Air Ducts

They are air’s passageway through an AC system. Having an air duct collapse will block proper airflow, which certainly lead to your ac freezing up, among other things. 

If Your AC Is Frozen, Try These Fixes First Before Calling An HVAC Professional 

Darn … your AC unit frozen. What now?

Before calling for help, try these steps. You may save some time and money.

First Things First

Turn the air conditioning system off using your thermostat (but first, be sure that the thermostat is providing power to the system). This stops the cooling. Now switch the fan on. Not auto, on. It will blow warm air onto the coil and speed up the defrost.

Now wait. Give the frozen evaporator coil, and/or refrigerant line time to thaw. This may take up to a full day in extreme situations.

You want to make sure the frozen refrigerant does not make it to the compressor. That would be bad. The compressor is only built to receive hot vapor. And they aren’t cheap.

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Second, Check For And Replace Your Dirty Air Filter

Even a little dirt can lead to insufficient airflow.

If your air filter looks unclean, get rid of it. And make sure to replace your filter with a clean one. You don’t want the dirt from the air accumulating on the coil. This would lead to your AC freezing up.

Third, Inspect Your Vents

Look for anything that may be blocking them on either side and clear it away. Check every room for shut vents – there may be a closed supply vent in an obscure corner you forgot about.

Last, It’s Time To Turn The HVAC System On Again.

Run it normally and keep an eye on it. If you see ice forming again, turn it off but turn the fan on so the ice can melt. Then call an HVAC technician.

Of course, to best way to eliminate issues such as an AC line frozen solid is to prevent them from happening.

How Do I Keep My Air Conditioner From Freezing Up?

As we mentioned before, anything blocking regular AC airflow will leave your AC freezing up.

The easiest and simplest things to do to prevent a frozen air conditioner is to change your filters regularly. This means from 4 to 12 times a year depending on the type of air filter, how many people live in the same household, and if there are pets.

Next, set a preventative maintenance plan in place. Have an HVAC professional inspect your AC system in the spring, before the sun is out in full force. Air conditioning service  can prevent a frozen air conditioner and other AC repair issues, as well as extend the life of your HVAC system.

The technician will check: your air filters for dirt, your coils for grime, your refrigerant level for leaks, your drain for blockages, and your blower fan for proper rotation and speed. Explore all the ways AC tune ups can benefit you in our blog about them!

Lastly, and more importantly, the HVAC pro can evaluate your air ducts for proper airflow. Sometimes this is hard to do because of how complex and hard to get at your air ductwork system is. There are many ways for the air flow in your air ducts to be inhibited (see our blog on air balancing). Having your ductwork checked in the spring and in the fall will help prevent an issue from popping up that could cost you big money.

Stay Chill With an aC repair

To Recap:

Your AC has a special chemical called a refrigerant that is vital to cooling your home. If the refrigerant gets too cold, you’ll notice your AC freezing up. Even on the hottest of days.

Always plan ahead and properly maintain your AC system. Look for the signs that something is not right, and when you notice something awry, don’t wait to act or the problem will worsen.

If you live in Maryland and you need fast, cost effective, and friendly service, SuperTech is the best AC repair company you will find! Schedule online or give us a call today so we can assist you.

We’ll assist you with any of your HVAC troubles. Even if it means we’re out in the hot sun looking at your frozen AC unit. And if your AC won't turn on, we have a blog discussing troubleshooting methods for it!

  • Really appreciate how simple you wrote this article. It’s easy to understand which is nut bueno for someone like me.

    • Great question! It can be as simple as needing a replacement filter, clogged condensate lines, or as drastic as collapsed air ducts and low refrigerant level. To determine the exact cause, we recommend turning your system to fan only until a licensed technician can diagnosis the problem.

    • Thanks for reaching out! It’s definitely possible that an incorrectly sized condenser could contribute to issues like freezing. When your condenser unit is not properly matched with the coil, it can cause imbalances in the system’s airflow and refrigerant levels, leading to inefficient cooling and potential freezing of the coil. A mismatch between the condenser and coil can result in the system overworking itself to try to maintain the desired temperature, which can ultimately lead to problems like freezing. Additionally, inadequate airflow caused by mismatched components can exacerbate the issue by preventing proper heat exchange.

      If you suspect that your AC company installed the wrong sized condenser for the coil, it’s essential to address this issue promptly. Contacting a qualified HVAC technician to assess your system’s configuration and make any necessary adjustments or replacements can help ensure optimal performance and prevent further issues down the line.

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