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What Causes An Air Conditioner To Freeze Up?

What causes an air conditioner to freeze up

After a long day of working, running errands or playing outside on a hot day, nothing feels better than that blast of cool air from the AC—until it freezes up. It seems impossible for anything to freeze as the temperature climbs, but this is actually a common occurrence. What causes an air conditioner to freeze up even when it’s hot out?

There are a number of possibilities.

Refrigerant Could Be Low

Refrigerant is the substance that keeps your air conditioner’s evaporator coils cool and transforms your indoor air from humid and hot to dry and cool. When this compound leaks, it results in lower pressure in the evaporator coils. The lower the pressure, the lower the temperature, which eventually causes a frozen coil and AC unit. Due to the potential health risks for you, as well as other members of your household, if you suspect you could have leaking refrigerant, it’s best to reach out to a professional as soon as possible.

Not Getting Enough Airflow

Your AC needs warm air from your home in order to stop naturally-forming condensation in the system from turning into ice. Dirty air filters and blocked ducts are commonly responsible for these issues. Air filters are something most homeowners take care of on their own, while airflow issues often do require a more extensive troubleshooting process by an experienced AC technician.

Coils That Are Dirty

Generally, the condensation that forms on the coils drips off or becomes absorbed. But if the coils are dirty, the water may stick around longer. This can lead to the coils becoming waterlogged and eventually freezing which would prevent airflow. Usually, routine maintenance performed by a qualified professional can prevent this from happening.

A Blower Motor That Isn’t Working

The blower motor provides the force that both sucks in warm air from the house and then pushes that air through the AC unit. If the air is not flowing properly through the unit, the condensation on the coils will not drip into the drip pan and moisture will be stuck and left to freeze. If you feel no air coming out of the vents outside of your home, you might have a problem.

A frozen air conditioner can really put a damper on a hot summer day. But a professional AC technician will know what it takes to get it up and running again—as well as how to maintain your unit so you’re less likely to have problems like this in the future.

If you’re going to go the do-it-yourself route, there are a couple of things you can take to get your AC up and running again. Keep in mind that AC units are complex and often the most cost and time effective options are calling in someone who deals with air conditioners day in and day out.

Evaporator coil freezing up

Evaporator Coil Freezing Up? Here’s What To Do

We touched on this above, but let’s dive into the specifics of evaporator coils freezing and potential ways to solve the problem. First, though, a bit about AC units.

Air conditioners don’t just cool the air—they also dehumidify the air in your house. Without your AC, the sticky and muggy summer air would linger in your home, making everyone uncomfortable. On the other hand, if you don’t know how many tons of AC per square foot you need for your home, you may have an oversized unit which could negatively affect the dehumidifying process.

When humid and hot air enters the air conditioner, it goes through an evaporator coil, which cools the air. The immediate blast of cold temperature turns the water vapor in the air to water droplets, or condensation. This condensation builds up on the outside of the evaporator coil and is collected in a drip pan.

Once the air has gone through the evaporator coil, it should be dry and cold—unless the evaporator coil freezes up.

Certain parts of the AC unit may prevent the moisture from going through the condensation process. If your evaporator coil is freezing up, you’ll can try doing a few things before calling in an AC repair person.

Check Your Filters

Air moves through the entire AC unit, but has to go through filters. The air filters provide your home with clean air, filtering out dust, dirt and debris.

If your air filters are clogged, warm air stops at the filters and can’t move through the unit.  Even if there is only a small layer of dust, it can still affect how much air gets to your unit. If there is no air moving through the filters, the evaporator coil won’t have any heat to absorb. Therefore, any moisture on the coil won’t get heavy enough to form into droplets and will eventually freeze. This will then cause the coil to freeze.

Empty The Drip Pan

The drip pan is where the water collects. If the drip pan is full, there is nowhere for the water to go. All of that extra water will end up freezing up due to the temperature of the evaporator coil area.

Have The Coils Cleaned Or Checked

After a long period of use, the evaporator coil can develop a layer of dust and dirt. Water droplets can cling to that dirt when they appear on the coils. This will prevent the water from falling into the drip pan, causing a blockage and eventually a frozen evaporator coil.

The wrong coil, or a broken coil that no longer works, can also cause an AC to freeze up and stop working. A heating and cooling specialist can help you determine whether you need a replacement coil or whether you need a whole new AC unit.

These three questions will solve most of your frozen AC problems, but it won’t solve all of them. Sometimes, AC units freeze up just because they’re a little chilly.

AC unit freezing up at night

AC Unit Freezing Up At Night? Here’s Why

While many of the reasons why your AC unit freezes up at night also apply to the daytime hours, one reason why your AC is freezing up solely at night is that most air conditioning units are only able to run in warmer temperatures. Once the temperature dips below 60 degrees outside, the AC unit may become ineffective or even freeze up. This is because as the temperature drops, so does the pressure within the unit and it could cause your AC unit to freeze at a faster rate.

You’re most likely not going to see thermometers in warmer climates drop down to 60 during the dog days of summer, but at nighttime, things can get a little cooler. If nighttime temperatures are set to reach even 65 degrees, consider putting the AC in “fan mode” or turning off the AC unit and opening up a window. You’ll still get airflow without your AC unit going into overdrive and risking it freezing up at night.

A malfunctioning thermostat could also be causing your AC unit to freeze at night. If your AC doesn’t stop running at the temperature that you have it set to, it could cause your system to work harder than it needs to and freeze your coils. While this could also happen during the day, if you sense that your home is too cold you are likely to check on it. When we’re sleeping, it’s easier for our system to go into overtime without us noticing.

If your unit is frozen, whether it’s just at night or during the middle of the day, you are likely going to want to know how to get it up and running again as soon as possible.

How to unfreeze AC unit

How To Unfreeze An AC Unit

The first question you should ask yourself is, “Have I replaced the filters lately?”

You’ll want to replace or clean your AC filters every month or so during the hottest months of the year. If your unit is in constant us, if you have furbabies or if you live in a dusty area, you may need to check your filters more often.

If you had your air filters replaced recently, the problem could be an issue within the coils. Turn the air conditioner off to give the coils and drip pan area time to defrost. At the same time, turn your fan setting to “ON”, as this will force your indoor AC fan to blow warm air non-stop over your AC’s frozen coils.

Before trying either of these methods, we highly recommend clearing out your drip pan. As your system defrosts, all of that ice will turn into water and if the pan is nearly full before this happens, it could lead to additional problems.

Once you have given the AC unit time to defrost, wipe excess moisture from your coils then turn it on again. Sometimes, all your system needs is time to rest and regroup—and, of course, unfreeze. Once that happens, it’s ready to go.

If this doesn’t work, it might be time to call in the professionals. Broken or leaky parts may require replacement, and you don’t want to mess around with expensive AC parts and end up damaging your system even more.

This is often a last-resort option, but when things get hot, the efforts of repairing or replacing your unit will be worth the reward of having cool, crisp air in your home again.

As a general rule, homeowners should schedule an appointment to have their AC system serviced twice a year to highlight any potential problems and check all the unit’s critical parts and components.

Once you know why your AC froze and what you can do about it, you probably now want to know how long you have to wait until you can start blasting that cool air back into your home.

AC frozen how long to defrost

AC Frozen: How Long To Defrost?

Once you turn off the AC, replace the filters or take any steps to fix the problem, plan a day trip to the pool or maybe head to the movie theater and have a marathon.

Why? Because it can take up to 24 hours for a frozen AC to defrost and start working properly again.

However, that’s not always the case. If you catch the problem before the system gets completely iced over, you might only need an hour to defrost—it all depends on the extent of the problem. But you probably don’t want to sit at home and take that chance in the sweltering summer heat. Assume you’re not going to get air conditioning for at least a day and get out of dodge.

ABC Can Resolve Your AC Problem

Unfortunately, not having air conditioning isn’t exactly an option when temperatures here hover in the triple digits for weeks at a time. Worse, if you opt for the do-it-yourself method and make a mistake, you could end up causing a worse problem that costs more and leaves you in the heat for longer. ABC’s experienced technicians can not only diagnose your issue, but they can also repair, replace or install any new equipment you may need. Whether it’s an urgent matter that requires immediate attention, or you just need regular maintenance, our skilled technicians can help.

Tom Riggs

Tom Riggs is the Division Manager for Mechanical Services, overseeing sales and operations for HVAC, Plumbing, Electrical, Appliance Repair and Water Quality for all ABC Austin branches. He joined ABC in 2014. Before ABC, he was an HVAC Service Technician, HVAC Comfort Advisor/Sales and Operations Manager. Tom attended Universal Technical Institute. He's an avid outdoorsman and enjoys country living with his wife and two sons.

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