How to unfreeze AC unit fast? [8-Steps to defrost air conditioners]

If you want step-by-step instructions on how to defrost your A/C unit, this article has got you covered.

This guide will go over the 8 simple steps to unfreeze your AC unit and get your home cool and comfortable again!

As a licensed HVAC contractor, I run into frozen air conditioners almost everyday throughout the summer.

A lot of the time it’s a simple maintenance related issue that caused the system to freeze up in the first place. If you’re having issues I always recommend having a technician check things out for you, but there’s definitely some troubleshooting you can do yourself.

Open Access Door To Verify A Frozen AC Unit

I recommend that homeowners first verify that the air conditioner is actually frozen. 

When AC’s freeze up, the air from the vents will usually be warm or have very little airflow. This happens when the evaporator coil is frozen, because it blocks air from the blower from pushing through the supply ducts. 

Sometimes you can get into the coil from an access door to see it, but not all the time. If you can’t see your coil, you can check your refrigerant lines and service valves on the outdoor air conditioner unit and look for ice or frost.

If you see ice it’s best to shut your system down to prevent any damage to the compressor. Replacing your compressor can be almost as expensive as replacing the entire unit, so preventing this is essential.

RELATED: What Causes The AC To Freeze Up?

Prepare For Melt Water With Towels

The amount of ice that forms on your coil can be pretty significant.

When we thaw or defrost the unit, quite a bit of water tends to leak out. The condensate drain attached to the coil should take a good bit of the water as long as its not plugged in, but it won’t take all of it.

Don’t be surprised if even before you begin thawing your system that you see water on the floor. Be prepared for a mess around the indoor unit. Having some towels or rags close by will be helpful.

Supplies & Tools You’ll Need

  • Towels or Rags – For cleaning up water as it thaws
  • 1/4″ or 5/16″ Nut Driver – For removing evaporator coil door

How To Defrost An AC Unit (8-Steps)

Step 1 – Turn Your A/C Off

Turning off the A/C will prevent additional ice from forming. Switch the mode on the thermostat from “cool” to “off”.

Step 2 – Turn The Fan On

Now that the A/C is off, we need to continue moving warm air through the coil to help it thaw quickly.

Most thermostats have a fan button. Switch it from “auto” to “on” to allow the indoor blower to circulate.

Step 3- Remove Evaporator Coil Door

Most A/C systems have a coil access door that can be removed to inspect the coil.

Almost all of them are fastened with 1/4″ or 5/16″ screws. Remove the screws and the door so you can see how much ice there is on the coil.

If your system does not have access to see the coil, don’t worry. You’ll know when all the ice is melted as soon as the water stops draining.

Read Also >> How To Check If A Thermostat Is Bad?

Step 4- Turn On Your Furnace (Optional)

If you really want to defrost your A/C fast, switch your thermostat to heat and turn the temperature up.

This usually melts the ice away very quickly, but can make a bit more of a mess because of how much water there is to deal with. Also know that you’re going to heat up the house for a short period of time while doing this.

This step certainly shortens the amount of time it takes to melt the ice, but isn’t necessary if you have the time and patience to wait on it to thaw naturally with just the blower running.

Step 5 – Remove And Check Your Air Filter

As mentioned above, a dirty filter is a very common culprit for an AC frozen coil. This is a great time to check it and replace it if needed.

Step 6- Put The Coil Door Back On

Once you see that all the ice is melted and the water has stopped draining, reinstall the access door and fasten with the screws that were removed.

Step 7 – Turn The A/C Back On

Switch your thermostat back to “cool” and turn your fan back to “auto”.

Keep an eye on things and if you see your system start to freeze up again, it’s probably a refrigerant related issue and you may need to call an HVAC contractor or technician to check things out for you.

RELATED: Why Your Air Conditioner Smells Musty?

Step 8 – Clean Up

Hopefully at this point everything is back up and running and your house is nice and cool. All that’s left is cleaning up the water on the floor around the indoor unit.

3 Main Causes of an AC Unit Frozen Over

Cause #1 – Dirty Air Filters

dirty or clogged filter is one of the most common reasons for your system to freeze up. 

The filter is designed to clean the air moving through your duct and into your house as well as keeping your equipment running clean and efficient. Airflow is very important for the A/C to function properly.

Poor airflow allows the refrigerant temperature to drop below freezing and the moisture that forms on your coil freezes. Once this happens, it restricts airflow even more and causes even more ice to form.

Types Of Filters

Most HVAC systems have a 1″ or a 4″ air filter. Thinner filters should be checked on a monthly basis and larger media filters should be checked at least every 6 months.

A lot of filter manufacturers claim their filters can last a lot longer than they actually do. In fact, the more expensive filters typically use a heavier material and need to be checked more frequently because they clean the air better and get dirtier faster.

If you choose to use a better filter with a higher MERV rating for better air quality, be sure to check and change your filter more frequently to prevent your A/C from freezing up.

You can read our guide on choosing the right air filter rating here.

Cause #2 – Dirty Evaporator (Indoor) Coil

Your A/C system has two coils, one inside and one outside.

The indoor coil is called the evaporator coil. Cold refrigerant is moved through the inside of the coil while warm air from the house is moved around it. The warm air from the house is absorbed by the cold refrigerant and carried outside to be rejected through the outdoor coil. 

If the warm air cannot pass through the coil properly, it allows the cold refrigerant to become too cold and again, ice will begin to form.

The underside of the coil can also become quite dirty. Using an evaporator coil cleaner can help keep things clean and make sure enough air is moving. A no rinse foaming cleaner is typically best for this. recommends that the evaporator coil be cleaned every two months.

Cause #3 – Refrigerant Problems and Ice

If a dirty filter or a dirty evaporator coil aren’t the cause of your ice, you probably have a refrigerant related problem.

Your system may be low or have a restricted metering device. In another article I talk about how to add refrigerant to the A/C, so if you’re interested in doing that, definitely check it out!

Otherwise, you’ll need to call a professional to properly check your A/C pressures and diagnose what type of problem you have.

What If The Outdoor Air Conditioning Unit Is Frozen?

Ice starts to form on the indoor unit when running in A/C and will travel all the way to the condenser outside as it continues to run. Once it shuts down the ice will naturally melt from the warm summer temperatures.

If the entire unit is frozen, you most likely have a heat pump and you’re using it for heat. Heat pumps often freeze up, and most of the time small amounts of frost on the coil are normal and will melt with the AC defrost cycle. 

If you have extremely thick ice build up, you may have a bad defrost board or defrost sensor. Defrosting the outdoor unit in the winter can be time consuming. Unless the temperature outside is above freezing, it will not thaw on its own and you’ll most likely have to do it yourself.

I typically turn the system to air conditioning to help warm the coil and use a garden hose to help melt the ice away. 

RELATED: What Is The Best Temperature For AC in Summer?

Frequently Asked Questions

How Long Will It Take?

In my experience, if left to defrost naturally, I’ve had it take up to 6 hours.

It varies a lot depending on how large the coil is, how thick the ice is, how warm the air in the house is, and so on. When I turn the heat on, I can typically have the entire thing thawed in about 30-45 minutes.

What Are The Main Reasons For Freezing?

Several things cause it to freeze up. Most common is poor airflow from a dirty filter.

You can also have a refrigerant issue or simply someone set the temperature on the thermostat too low. If you’re running your A/C consistently below 66*F, there’s a good chance it’s going to freeze up.

Is It Okay To Pour Hot Water On It?

I don’t recommend this. There’s not a lot of space to get into an evaporator coil and attempting to pour hot water in a tight space isn’t going to end well.

You’re likely to get burned or miss and pour water all over your equipment.

If the ice you’re trying to melt is on your outdoor unit, then yes. The outdoor unit is built for the weather and there’s a lot more space to safely pour water.

Will It Unthaw By Itself?

Only if the thermostat was set too low. Ice is not supposed to be present while running your A/C.

If ice formed once, it will most likely happen again if nothing changes.

How To Thaw A Window A/C Unit?

To defrost a window AC unit, turn the fan setting from ‘auto’ to on which will melt any ice buildup. After all the ice is melted, turn the fan setting back to ‘auto’ or ‘cool’.

Final Thoughts

Frozen AC systems are extremely common and even happen to small window A/C units. Regularly maintaining your system is your first line of defense to prevent it from happening. 

If you happen to have an iced up A/C, don’t panic. Start with the filter and shut your system down for a little while.

Follow these steps and your likely to get everything back up and running. If you find yourself struggling or if it keeps freezing, call a professional and get it checked out.

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