If your AC is frozen, you will need to unfreeze it. It is not all that obvious how to defrost the AC unit. That’s why we are going to explain how to unfreeze an AC unit. Note: Always turn off a frozen AC unit. Running it might damage the compressor, and compressor replacement is the costliest AC repair job.
In more than 90% of cases, when AC is frozen the part that really needs to be unfrozen are the indoor evaporator coils. These are cold coils; when they get too cold or when there is a lack of airflow, they will freeze over and we will have a frozen air conditioner. You can check how to tell if your AC is truly frozen (signs) here.
When we talk about unfreezing an AC unit we are talking about how to thaw the ice off of frozen evaporator coils.
Here’s the deal:
Given enough time, the AC unit will unfreeze itself. However, in most cases, we want to unfreeze an air conditioner as fast as possible. The problem here is that the latent heat of ice – heat required to melt ice – is very high. In fact, you will need 336 kJ of energy (equivalent to about 80.4 kcal) to melt 1 kg of ice. That is equal to 152.4 kJ of energy to melt 1 pound of ice.
How to unfreeze an AC unit fast(er)?
Here is the outline of 4 ways how to can thaw frozen evaporator coils at different speeds. Some you can use, others you should avoid:
- Unfreeze the AC unit naturally. This just involves doing nothing. In a day or so, the ice on the evaporator coils will thaw itself. But we usually don’t want to wait for a whole day or even more before we can start using an air conditioner again.
- Unfreeze the AC unit with a fan only mode (or even turn on the heat in mini split heat pumps). Here we shut off the flow of refrigerant and only run the indoor fan. The warm airflow will melt the ice on the indoor coils in 0.5-2 hours.
- Unfreeze the AC unit fast with a hair dryer. How to unfreeze the AC unit fast? You can use a hair dryer to speed up the process of unfreezing an AC unit. With correct use (not too high temperature; we are going to explain that further on), you can unfreeze evaporator coils in under 1 hour (down to 10 minutes).
- Unfreeze the AC unit too fast. The quickest way to unfreeze an AC unit would be using a blow torch to thaw the ice. This is advised against because it might crack the evaporator coils. Other such methods that might be useful in limited situations are of ‘Can I pour hot water on frozen air conditioner?’ variety. Hot water can be used to thaw a frozen outdoor AC unit but is not a suitable method to thaw a frozen evaporator coil, for example.
We are going to cover each of these AC defrost methods in turn to create a complete overview of how to unfreeze an AC unit. Most homeowners will likely know the #1 method (natural defrosting) but that’s too slow in many cases. We will explain why the #4 methods (using a blow torch or hot water) will likely damage the evaporator coils.
The most useful techniques of how to quickly unfreeze an AC unit are the #2 method (using a fan and warm airflow) and the #3 method (using a blow dryer to unfreeze the AC unit fast). It is recommended that you focus on these two but, as explained, we will start with the natural defrosting in order to cover this topic as thoroughly as possible:
How To Unfreeze AC Unit Naturally (#1 Method)
The easiest way to unfreeze the AC unit is just to leave it alone. Here we presume two obvious things:
- Indoor temperature without the AC on is at least 77°F.
- Temperature of the ice is 32°F.
The ice on the evaporator coils will thaw. In time. This ‘In time’ is usually the problem here. Obviously, we know that the ice will melt at room temperature. However, during hot summer days, we do need air conditioning every day.
We usually don’t prefer waiting until the AC will be unfrozen all day long (or even more). The thawing process here is simple to understand: Warm air will naturally warm up the ice and, in time, melt it.
Understanding this process, we can speed up unfreezing the AC unit by:
- Increasing airflow (#2 method).
- Increasing airflow temperature.
- Combining an increase in airflow and an increase in airflow temperature (#3 method).
Here is how we can use the functionality of AC units in order to help the air conditioner defrost itself:
How To Unfreeze AC Unit With Fan Only; Or Optional Heating (#2 Method)
The most convenient quick way to defrost an AC unit is to use the fan-only mode. Without the fan, the airflow naturally reaching the indoor evaporator coils is 10 CFM or less. By turning the indoor fan on, you increase the airflow thawing the AC unit up to 500 CFM or even more. In effect, 50x or more air is being used to defrost the ice on the coils.
Here is how you defrost the air conditioner by turning on the fan:
- Important: Make sure that you leave the air conditioning (‘Cooling’ mode) off. You don’t want the refrigerant flowing; you only want to turn on the indoor fan motor that will spin the fan.
- Turn the AC fan setting from ‘Auto’ to ‘On’. This is the key step here; when on ‘Auto’, the indoor AC fan won’t run if your AC is frozen. By switching it to ‘On’ mode, the fan will start pushing warm air over the frozen coils.
- You will see the brownish ice on the coils melt. This happens quite quickly; the AC should be completely defrosted in under 1 hour.
Do note that all that melted ice is now being turned into water. That water has to be drained. After all the ice is gone (running fan on ‘On’ mode for about 1 hour), wait for 30 minutes in order to ensure all the water is adequately drained. Only after that 30 minutes, you should turn the AC back on.
Heat Pumps: If your AC can heat in the winter, you can switch from ‘Cooling’ mode to ‘Heat’ mode. This is to heat the indoor evaporator coils from within the coils (hot refrigerant). The heating mode can defrost an AC unit in less than 15 minutes.
How To Unfreeze AC Unit Fast With Hair Dryer (#3 Method)
If you want to unfreeze your AC unit fast, you can use a standard hair dryer. You do have to be careful temperature-wise and distance-wise in order not to crack the evaporator coils.
Here is why a hair dryer can defrost the coils so quickly:
- You are increasing the airflow to the coils rapidly (500+ CFM).
- You are increasing the temperature of the airflow over the coils (Up to 20°F higher air temperature).
Now, you have to be careful not to overdo it with the hair dryer. Namely, coils are frozen, and introducing heat very rapidly might damage the coils. Example: Never use the dryer on the ‘High’ setting at the point-blank range.
The safe way to unfreeze AC units is to set the hair dryer to a ‘Low’ setting and point it at the evaporator coils from at least a 10-inch distance.
Note: You should be blowing hot air directly over the coils. That means you will have to expose the coils by first unscrewing the air handler cover and then removing the access panel to get to the coils.
With a hair dryer, you can defrost your AC unit in about 10 or 20 minutes (depending on the size of the coils and the amount of ice accumulation).
How Not To Unfreeze AC Unit (#4 Method)
The last method – the quickest way to unfreeze an AC unit – is the one that works in theory but should never be used in practice. It includes using heating elements that unfreeze the coils too fast.
Namely, a lot of homeowners are interested if you can pour hot water on frozen coils or if you can use a blow torch, burners, and so on to thaw the ice. Obviously, hot water, burners, and other powerful heating methods will unfreeze the air conditioner in seconds. However, despite their effectiveness, they should not be employed to defrost AC units.
We are trying to thaw the ice on evaporator coils. If we do that too quickly, these coils – made out of durable metals with superb thermal properties – might crack. Cracking a coil, filled with a refrigerant gas or liquid, is never a good idea.
That’s why pouring hot water over the coils is strongly advised again. Yes, you will see the ice disappear in a matter of seconds, but you could damage the AC unit quite severely.
Exception for outdoor units: If your outdoor AC unit is frozen due to very low winter conditions, you can use hot water to unfreeze it. The outdoor AC cover – made out of aluminum or hard plastics – won’t crack. And even if it does crack, you don’t really need to repair it since it doesn’t affect the running of the AC unit significantly.
All in all, there are several ways how to unfreeze your AC unit. You can leave it alone and wait for a day, use fan only mode or hair dryer. Just be careful about thaw methods that might increase the temperature too quickly and crack the evaporator coils.