How To Unfreeze an Air Conditioning Unit

It may be useful to know how to unfreeze an air conditioning unit if it becomes frozen and is impacting your indoor environment making things uncomfortable.

This is surprisingly common during the hottest days of summer.

frozen air conditioningWhen an AC unit freezes up, the unit will no longer be able to cool the air to the required temperature inside your home.

That can mean that the interior will become warmer and eventually uncomfortable.

However, all is not lost. The good news is that it is possible to quickly unfreeze an AC unit, whatever it's configuration.

That includes regular or self evaporating portable units where the reduction in internal moisture through auto-evaporation is not enough to prevent some freezing. Same goes for window AC units as well as larger fixed mini-split AC units.

Let's take a step-by-step procedure that you can follow on how to get the problem fixed. I will also explain some things that you can carry out that will prevent the AC unit freezing up again some time in the future.

Unfreezing an AC Unit

To unfreeze the AC unit, follow this surprisingly simple process that you can use to complete the task and have your AC working again.

It's worth noting that it can take about 24 hours to remove all the ice from the unit's components and allow it to return to normal working condition.

  1. Turn off the AC unit's thermostat

    Doing this will make the job go smoothly while unfreezing the unit. Warning: If you fail to turn the thermostat off, the unit will keep sending the excessively cold refrigerant to the outside unit and hamper the process of thawing the coils.
  2. Turn on the fan

    Doing this will help to thaw the coils' surfaces fast. The fan will blow a stream of warm air continuously over the coils, melting the ice accumulated on their surface.
  3. Check the air filter

    A dirty, clogged air filter can often be the culprit that caused the AC to freeze up. A blocked air filter greatly reduces airflow through the system. This will cause the AC components to overwork and try to compensate for the lack of airflow by super cooling the refrigerant. Check the state of the air filter and if it is dirty, replace it with a new filter.
  4. Check for any other faults

    A faulty thermostat, blocked drainage and low refrigerant levels are among the more common technical faults that can cause freezing up of the AC. Unfortunately, these problems may be too complicated for an unqualified person to solve by themselves.

If, after following the first three steps the unit has not thawed after some time, the cause may be one of the problems listed in the fourth step. If this is the case, it may be best to call a certified technician to locate, diagnose and fix the issue to get your AC working properly again.

Why Do Air Conditioners Freeze Up?

There are a number of reasons that an air conditioner can freeze up.

Most of the time, if the thermostat has not been set at much too low a temperature or there is not an obvious blockage in the airflow, mechanical faults can be the cause. Occasionally, low refrigerant levels inside the unit can be the cause.

Let's take a look at some of the more common things that can cause a frozen AC unit.

Thermostat Problems

An air conditioner relies on its thermostat setting to ensure it cools the space to the correct temperature level.

Human error can result in an incorrectly set thermostat at a very low temperature, causing the unit to overwork, resulting in the condenser coils freezing up on the outside as condensate is chilled to below freezing point.

Check the thermostat setting first of all to ascertain the correct temperature is set. For most normal circumstances, this should be around the 70°F (20°C) mark for a comfortable environment.

If, on the other hand the thermostat is faulty, there is no way for the air conditioner to accurately cycle off and on. What often happens in this case is the air conditioner cools the insufficiently or excessively.

If there is insufficient cooling, the home will become uncomfortably warm. Excessive cooling will result in the unit's coils freezing up.

Drainage Problems

Frozen AC coils can lead to drainage problems and excessively dripping condensate.

Under normal operating, a multi-unit or self contained single unit air conditioner condenses water vapor from the air into its liquid form. However, this process can be interfered with when ice forms on and inside the coils and the air conditioner fails to drain the water properly.

This causes the AC to use far more power in its attempt to maintain a cool atmosphere in the home, usually failing to reach the set temperature caused by poor drainage.

Low Refrigerant Level

An efficiently functioning air conditioning system requires its refrigerant to be maintained at the ideal level. Should the level of refrigerant decrease dramatically, the cooling coils can become very cold.

Excessively cold coils will cause condensate to ice up on the outside and freeze inside. This causes a blockage with problematic results including the air conditioner's failure to maintain a comfortable climate indoors.

How to Tell an AC Unit is Frozen

There are a number of signs that will tell you an AC has frozen up.

It can be important to learn how to tell when an air conditioning unit has become frozen and it can help to save time thawing the system quickly before things get out of hand.

If you miss the telltale signs, much time could be wasted in troubleshooting the cause of the air conditioning system failure when the problem may simply be frozen up coils.

Here are some obvious signs to look out for that will point to a frozen up AC.

Ice Present in the AC

Locating ice particles on any part of an air conditioner is the first clear sign that there is freezing water inside the system. When an AC freezes up, the refrigerant temperature falls dramatically and the cooling coils become very cold.

Abnormally low temperature inside the AC components result in the formation of ice particles that settle on the parts. If you open up the AC and notice ice deposits inside the unit, this as a clear sign that you need to take action to thaw the AC.

Warm Air Coming Out of the Air Supply Vents

Placing your hand over the air supply vents will tell you if the air coming out is warm rather than cold.

This is a warning sign that you should check to see if the AC has frozen up. That's because this will cause a failure in cooling the air appropriately.

A Hissing Sound

The sound of hissing coming from the AC is an indicator that checking the unit for any freezing is a good idea. Just a hissing sound is not a clear sign of a frozen AC, but it should be followed up by checking the system for other signs anyway, just in case it is freezing.

Preventing the AC from Freezing in Future

While there is not much an unqualified person can do to prevent technical faults occurring within an air conditioning system, there some simpler actions that you can carry out that can prevent some of the more common causes of freezing in the AC in the future.

To begin with, one method of problem prevention is maintaining your AC in good working order. Contracting a qualified HVAC technician to perform regular maintenance is always worth considering.

Here are some tips you can use to keep your AC running smoothly and even prevent it from freezing up.


While there will be instances where a freezing up AC is caused by technical faults beyond the capability of an unqualified person to deal with, there are some common causes that can be identified and dealt with by most people.

It is possible to prevent the AC unit from freezing up and remedying the situation if freezing has occurred by following the steps and tips laid out above.

The procedures can pertain to all types of refrigerant-based cooling units, including portable wi-fi enabled air conditioners, commercial heavy duty portable air conditioners and the types of PTAC or VTAC units that can be found in hotels, motels and health centers, for example.

If the problem seems to be beyond your capabilities to remedy satisfactorily, call a local HVAC technician to solve what could be a more complicated issue, rather than waiting and hoping it will fix itself, which more often than not, it will not!

Note: This information does of course not pertain to non-refrigerant-based air coolers such as the "no vent required" genre of evaporative (swamp) coolers which do not contain refrigerant or condenser coils.

Posted: June 20, 2021

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