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Is your AC frozen up into a block of ice?
Fortunately, getting an AC thawed out is a simple (but rather long) process.
The other part of the equation is figuring out why your AC froze up in the first place.
An AC that’s freezing up usually has one (or both) of these two problems:
- Airflow issues
- Refrigerant issues
In this article, I’ll go over what you should do when your AC freezes up. I’ll also go over all of the causes of a frozen AC—so you can prevent your AC from freezing up again.
What to do when your AC is frozen
If you find your AC frozen up, your first order of business is getting it thawed out and running again.
Hopefully, the cause of your frozen AC is something simple like a dirty air filter.
In the worst case, your AC might be frozen due to an issue in its refrigerant system (I’ll go over refrigerant issues in a section below).
Follow these steps to thaw out your AC and get it running again:
- Change your AC’s air filter
- Look for possible air blockages
- Thaw out your AC
- Run your AC and observe its behavior
Change your AC’s air filter
If your AC is frozen, the first thing that you need to do is change its air filter.
Why do you need to change your AC’s air filter if your AC is frozen?
Because a dirty air filter is one of the most common causes of a frozen AC.
Changing the air filter is also one of the easiest maintenance tasks that you can do on your AC. Even if your AC isn’t frozen, you should do it anyway.
When changing your AC’s air filter, take a look at how dirty the old filter is before throwing it away.
If the filter has layers of caked-up dust on it, there’s a good chance that the airflow restriction from the dirty filter caused your AC to freeze up.
Look for possible air blockages
After changing your AC’s air filter, the next thing to do is look for air blockages at your air vents and registers.
Begin by taking a look at the vents and registers inside your home.
If a piece of furniture blocks the flow from an air vent, your AC can freeze up. Move any objects that are obstructing airflow from your vents.
Next, take a look at your ductwork and dampers. Look out for collapsed ductwork, air leaks, and closed dampers. If you have flex duct, make sure they’re not damaged or collapsed.
Thaw out your AC
The good news is that thawing out your AC is a simple process.
The bad news is that it takes quite a bit of time—usually a few hours.
To best way to thaw your AC is to run it in “Fan Only” mode. Running your AC in Fan Only mode disables its cooling and circulates room-temperature air through your AC.
After a few hours, the ice on your AC’s evaporator coil will melt away.
If this method takes too long, you might be tempted to speed up the process by using a hair dryer, hot water, or even a blow torch directly on the frozen coil.
While these methods will certainly help defrost your AC, I don’t recommend them because they can damage your AC coil. The rapid temperature change from a stream of hot air, water, or fire can cause your AC coil to crack.
If you really need to speed up the process, the only method I recommend is the hair dryer. But only use it on the “Low” setting, and keep it at least 1 foot away from the coil.
Stop using the hair dryer when the ice is almost gone. You don’t want the heat from the hair dryer to come into direct contact with your AC coil. Let the fan finish off melting the ice instead.
Run your AC and observe its behavior
After you defrost your AC, the next thing to do is to turn it back to “Cool” mode.
As your AC starts cooling your home, take a look at the coil every hour or so to see if ice starts to form.
If your AC runs without ice formation, then your AC had an airflow issue that was fixed by changing the dirty filter and removing air blockages.
If you see ice forming, then your AC could still have an airflow or refrigerant issue.
I’ll go over all the different things that can cause an AC to freeze up below.
What causes an AC to freeze up?
Here are some things that can an AC to freeze up:
- Clogged air filter
- Blocked air vent or air register
- Collapsed air duct
- Blower issues
- Clogged evaporator coil
- Blockage in the refrigerant system
- Leak in the refrigerant system
I’ll go over them below.
Clogged air filter
A clogged air filter is one of the most common reasons for a frozen AC.
How does something so simple such as a clogged air filter cause your AC to freeze?
It’s all due to airflow.
A clogged air filter will reduce the airflow through your AC system.
When your AC loses airflow, it will absorb less heat from the air in your home.
If your AC doesn’t absorb enough heat, it will start to freeze up.
I recommend changing your AC’s air filter every 1-2 months, depending on how much you run your AC.
Blocked air vent or air register
Blocked air vents and air registers can also cause a frozen AC.
A blocked air vent or register produces effects similar to a clogged air filter—loss of airflow.
That’s why it’s important to never close off the air vents in your home.
Even if a room doesn’t need any cooling, you should not close off its air vent or you may starve your AC of airflow.
Objects in your home can also block the airflow through your air vents.
Here are a few things that can block an air vent:
So remember to keep all obstructions away from your air vents. And don’t go around your home shutting off air vents either.
Collapsed air duct
While collapsed air ducts are uncommon, it’s worth mentioning them because they can go unnoticed.
A collapsed air duct is a piece of ductwork that has “caved in” on itself. Think of it like sucking all of the air out of a paper bag.
So how does an air duct collapse?
A collapsed air duct is caused by too much negative pressure in the air duct.
So what causes the excess negative pressure, then?
Ironically, excess negative pressure is usually caused by a blocked return air vent. So that’s how one problem can lead to another.
If you have a collapsed air duct, then it will need to be replaced.
If it’s a flex duct, then the repair will be fairly simple. Flex ducts are available in different lengths and sizes, so the new piece will just have to be cut to length and installed.
If it’s a rigid metal duct, then the repair will be more complicated. Rigid ductwork is made of sheet metal and requires manual fabrication with tools. You’ll definitely want a professional to replace a rigid duct.
Your AC’s blower can have all sorts of issues that will cause your AC to freeze up.
Here are a few issues that your blower can have that will cause your AC to freeze up:
- Blower motor burned out
- Blower wheel broken
- Blower wheel is excessively dirty
- Blower’s fan belt snapped
- Blower motor overload tripped
- Blower motor capacitor bad
In any of the above cases, you’ll want to get your blower repaired or replaced.
So why do blower motor issues cause an AC to freeze up?
Any issue with a blower motor has the potential to cause an AC to freeze up due to airflow issues.
If your blower is not working, then your AC will freeze up because there won’t be any airflow going through its cooling coil. The cooling coil will get extremely cold without removing heat from your home.
Check out my article below for a step-by-step guide on what to do if your furnace’s blower motor isn’t working:
Clogged evaporator coil
The evaporator coil (also called the “cooling coil”) is the part of the AC that cools the air in your home. It’s made of a copper tube embedded within an array of small aluminum fins.
If the aluminum fins in the evaporator coil get clogged, your AC will lose airflow and may even freeze up.
The loss of airflow reduces the heat exchange between the evaporator coil and the air.
The reduction in heat exchange causes the evaporator coil to subcool below freezing temperatures—soon ice will begin to form on the coil.
A clogged evaporator coil is something that usually never happens—as long as your AC is maintained properly.
Here’s what causes a clogged evaporator coil:
- Running your AC without an air filter
- Not changing the air filter in your AC
- Air leakage around the air filter in your AC
So what should you do if your AC’s evaporator coil gets clogged?
You’ll need to clean it out.
Unfortunately, the evaporator coils on most ACs are hard to access. You may even need to cut open the sheet metal to access it.
Sometimes an air handler has a small access panel on it that you can unscrew and open up to get to the evaporator coil. Consider yourself lucky if you have one of those, it will make cleaning the coil much easier.
Once you gain access to the coil, you can try a few different methods to clean the coil off, depending on how dirty it is.
Check out my article below for a list of some of the best coil cleaners for your AC. The article also has instructions on how to clean the evaporator coil.
Blockage in the refrigerant system
Issues in your AC’s refrigerant system can also cause its coil to freeze up.
If your AC’s refrigerant has any blockages in its flow, its coil may freeze.
Why does that happen?
If there is a block in refrigerant flow, the reduction in pressure will cause your evaporator coil to get colder than it normally does. With enough pressure drop, the coil will get below freezing temperature, and ice will begin to form on the coil.
If your AC has a refrigerant blockage, it’s most likely in the metering device (such as TXV) or filter drier.
If you think a part in your AC system has a refrigerant blockage, one way to confirm is to measure the temperature across the part. If there is a large temperature drop (more than 1 or 2°F) across the part, then it likely has a blockage.
The exception to this test is the metering device—they will always have a large temperature drop. But if the temperature leaving the metering device is below freezing, then it likely has a blockage.
If your AC system has a blockage in its refrigerant system, then you will need an HVAC professional to repair it.
To repair the refrigerant blockage, the entire system will need to be drained of refrigerant. After the system is drained down, the part will need to be removed and then replaced or repaired. Finally, the system can be recharged with refrigerant and recommissioned.
Leak in the refrigerant system
A refrigerant leak in your AC can also cause it to freeze up.
If your AC loses refrigerant, it will operate at abnormal pressures. The pressure imbalance causes the evaporator coil to get much colder than it should, often achieving freezing temperatures.
As air flows through the freezing evaporator coil, ice forms and the coil freezes over.
So how do you know if you have a leak in your AC’s refrigerant system?
You can sometimes find a refrigerant leak by listening for a “hissing” sound coming from your AC’s refrigerant lines, devices, or coils.
The best way to confirm a leak in your AC system is to use a soapy water mixture. Spray a soapy water mixture in the area where a leak is suspected. If bubbles form in the area, then it has a leak.
But soapy water only works if you have a general idea of the leak’s location.
What if you have no idea where the leak is?
A good way to track down a leak is by using a refrigerant detector.
A refrigerant detector will find any signs of refrigerant leakage, so you only need to probe around the general area to confirm if your system has a leak.
This refrigerant leak detector will detect the presence of R22, R410A, and R134A. While it doesn't have the accuracy or features of more expensive leak detectors, it gets the job done for most people and comes at an affordable price point.
In any case, if your AC has a refrigerant leak, it will need to be repaired by an HVAC professional.
How to prevent your AC from freezing up
Once you’ve got your AC thawed and running again what do you do next?
You’ll want to take measures to prevent your AC from freezing again.
Here are some things that you can do to help prevent your AC from freezing:
- Change your air filter regularly
- Keep your air vents free from obstructions
- Get your AC serviced regularly
I’ll go over them below.
Change your air filter regularly
Changing your air filter is one of the best things that you can do to prevent your AC from freezing up.
By changing your air filter regularly, you’ll help keep your AC’s air system clean. It will also help keep your blower motor from overworking—further helping prevent freeze-ups.
A clean air filter also is less likely to collapse and let particles clog up your evaporator coil.
If it’s not already clear, changing your air filter is not only good for preventing freeze-ups—it also helps with the overall health and performance of your AC system.
Keep your air vents free from obstructions
Keeping your air vents free from obstructions is a simple thing that’s often overlooked.
If one of your air vents is blocked, it will inhibit airflow in your AC system—leading to a frozen coil.
In more serious cases, a blocked return air vent can also cause your ductwork to collapse.
That’s why it’s important to keep all furniture and objects away from your air vents and registers.
Also, don’t go closing off the dampers on any of your air registers—it will restrict airflow and contribute to more issues than it’s worth.
Get your AC serviced regularly
There are some things that you simply can’t take care of as a homeowner. Particularly, anything in your AC’s refrigerant system requires an HVAC professional to handle it.
That’s why it’s important to have an AC technician take a look at your AC unit at least once a year.
When an AC tech performs a service on your AC, they should measure your refrigerant system’s temperatures and pressures to ensure that it’s operating correctly.
If there are any imbalances, leakages, or blockages in your refrigerant system, then your AC tech will be able to find them and correct them before they turn into a bigger problem.