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4 Reasons Why Air Conditioners Freeze Up and What to Do If This Happens to You

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Last Updated on: January 9, 2024

You’re not seeing things: even during the hottest day of summer, it’s possible for your air conditioner’s indoor unit to form a layer of ice. This problem not only affects your AC system’s ability to cool your home, but it can lead to expensive repairs.

Below, our HVAC experts will explain why air conditioners form ice and what to do if this happens to you.


Below are the top reasons why ice forms on indoor air conditioning units.

Blocked Airflow

Your indoor AC unit contains a part called the evaporator coil. This metal coil has refrigerant running through it which makes it really cold. When your warm indoor air blows over the cold coil, it transfers its heat and moisture to the coil and becomes cool and dry (or conditioned).

So what happens when there is too little air blowing over the evaporator coil? Without all that heat from your indoor air transferring to the cold coil, ice can start forming on the metal. Blocked airflow typically results from a dirty air filter that needs to be replaced or something obstructing your return vent, like a box or piece of furniture.

Low Refrigerant Level

At first, ice caused by low refrigerant levels seems counterintuitive, but we’ll explain how it works. Remember the refrigerant that flows through the metal coil in your indoor AC unit? If your AC has been leaking refrigerant or if the technician who installed the unit didn’t charge the refrigerant correctly, your AC might not have an adequate refrigerant supply.

When your AC’s refrigerant is low, the pressure in the system drop, and the refrigerant’s temperature becomes much colder than usual. Consequently, when moisture from your indoor air condenses on your AC’s coil, the refrigerant makes the coil so cold that the condensation freezes. Ice then builds up more and more, restricting air movement through the coil, which makes the ice buildup even worse.

Dirty Coil

Sometimes the coil itself is the source of the problem. Without routine maintenance, your indoor AC unit can accumulate a lot of dust and grime, and the evaporator coil inside it is no exception.

Sometimes, a coil can become so dirty that it can block heat from transferring effectively to the refrigerant inside it. As a result, the already-cold coil will just get colder and colder until the condensation collecting on it freezes.

Damaged or Broken Blower Fan

Your air conditioner contains a blower fan powered by a motor. This fan’s job is to pull in warm air from your home and push out cool air from your AC unit

If there’s something wrong with the fan or its motor, your AC won’t get enough airflow to prevent ice from forming. Similar to the problems described above, the lack of air movement will cause the evaporator coil to get extremely cold and freeze the condensation it has collected.

Problems with the blower motor are fairly obvious. You’ll either notice that there’s little or no air movement coming out of your vents or that the fan can only blow at a certain speed (if it’s a two-speed or variable-speed model).


To answer the question you probably have now, yes, frozen air conditioners are a significant problem. Ignoring this issue can lead to a damaged compressor, which is a very expensive part to replace.

If you spot ice forming on your AC unit, do the following to prevent damage to your system:

  • On your thermostat, turn off the “cool” setting but leave the fan on (unless it’s broken—then contact an HVAC technician). This will allow warm air to circulate through your system and thaw the ice faster.
  • In the meantime, change your air filter. It’s safest to use a filter with a MERV rating no higher than 11. This is high enough to keep out allergens but low enough to allow enough airflow through most systems.
  • Make sure that all of your home’s vents are open.
  • Once the ice has melted (which should take about 3 hours), check to see if the problem starts again when you start running your AC as usual.

If your AC starts forming ice again, it’s time to call an HVAC technician to troubleshoot the issue.

Our professional technicians provide 24/7 emergency AC service in Centreville. Don’t hesitate to give Service Specialties a call for any air conditioning issue you are experiencing: (703) 968-0606.

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