Why Is There Ice On My Air Conditioner?

Frozen AC Unit

Ice on your AC unit often occurs when the refrigerant level is low or because air is not moving properly through the system. If you find ice on your air conditioner, turn it off immediately to allow it to defrost. This is the first step in troubleshooting the issue. 

A frozen AC unit can drastically reduce efficiency, which forces the air conditioner to work even harder to keep your home cool and comfortable. If the unit is running a lot more than usual and not actually cooling your home, there is a good chance your AC unit is covered in ice. A frozen air conditioner can also cause the system to stop working entirely. It is important to note that ice can form on your AC unit, even in the summer months.

What Causes Ice on an AC?

  1. Low Refrigerant: Refrigerant is also referred to as coolant, freon or R-22. If your refrigerant is low, this could mean you have a refrigerant leak. Low refrigerant causes lower pressure in the system, leading to lower temperatures. This is why ice begins to form on the AC’s evaporator coil. The best thing to do if you find yourself in this situation is to have a professional AC repair technician repair the leak and recharge the coolant levels. To prevent this from happening to you, it is always a safe bet to have your HVAC system inspected and serviced once a year to check refrigerant levels or catch any potential problems.
  1. Dirty Evaporator Coil: Dirty evaporator coils can cause your AC unit to freeze because air flow becomes restricted throughout the unit. A dirty coil can also force the air conditioner to use more electricity, which causes damage to the compressor. If you see ice around your HVAC unit, shut it off until the coil is professionally cleaned or replaced. To prevent your evaporator coil from getting so dirty, clean it regularly. 
  1. Mechanical Failure: There are several components of an air conditioner that can malfunction and cause your AC unit to freeze up, such as wiring issues, kinked refrigerant lines, broken valves, a clogged drain, and damaged fan. You should have a licensed HVAC professional come out to inspect and repair the unit as soon as possible. Having your unit regularly maintenanced, preferably in the spring and fall, can help to prevent your heating and cooling system from experiencing these issues. 
  1. Restricted Airflow Through AC Unit: Your heating and cooling system relies on airflow in  order to function properly. If there is too little airflow, the temperature can decline, causing the AC unit to freeze. Airflow can become restricted from the unit because of dirty air filters, ductwork clogs or leaks, and closed vents. There could also be an object or debris obstructing the outdoor unit. Depending on what exactly is restricting your airflow dictates the approach you should take to resolve the issue. Perhaps you need to change your air filter, clean out or repair your ductwork, or have specific components replaced entirely. During the seasons your HVAC unit will be used more frequently (like summer or winter), you should consider having your ductwork sealed, You should also change your filters once per month to help avoid airflow disruptions.
  2. Outside Temperature is Too Cold: AC units weren’t designed for use in temperatures below 62 degrees fahrenheit. If your system gets too cold to the point of freezing, turn it off to allow it to thaw out. To prevent this from happening, you can turn off your air conditioner at nighttime when the temperature is expected to be 60 degrees or lower.

How Does an Air Conditioner Freeze?

Air conditioners circulate coolant through the outdoor unit, which changes it from a gas to a liquid. Then, the liquid is pushed by a fan through the evaporator coil. The evaporator coil exchanges the thermal energy with the air surrounding it. This is when the refrigerant turns from a liquid to a vapor while removing heat from the air around it. As heat is extracted, the air cools off and is sent back into the house.

Then, the condenser reverts the refrigerant vapor back into a liquid, eliminating any heat. Once the liquid departs from the evaporator again, it is already a cool gas. That’s when it goes back to the condenser, for the cycle to begin again. This process continuously repeats itself as your home is being cooled. The system, when set to AUTO mode, runs as needed in order to reach and maintain the desired temperature set to your thermostat. 

Ice starts to form on your AC unit when the temperature in the condenser evaporator coil drops below freezing. This typically occurs when refrigerant is too low, or a refrigerant leak. This is most-commonly caused by dirty coils, broken fan, improper wiring, and clogged air filters.


Due to the chemical makeup of refrigerant, when heat is not absorbed into the coil for a specific period of time, it begins to freeze up. Preventin the presence of hot air around the coil means that airflow is being cut off somewhere in the system. Some possible causes could be: 

  1. Dirty Air Filter: Dirt and debris can sometimes black warm air from entering the return vent. Sometimes even a household object can get stuck in the vent and block the airflow. 
  2. Collapsed Air Duct: Less commonly, you may find that your air duct has collapsed due to poor installation, pests, or wear and tear. This means that it can no longer get the air to travel to the coil.
  3. Dirty Evaporator Coil: Sometimes the evaporator coil gets covered in a layer of build-up, preventing air from passing through. If dirt has found its way into this area, you could have a defective filter or cracks in your air duct.

How Do I Know If There is Ice In My AC Unit?

When there’s ice inside your AC unit, it can’t always be easily seen, but that doesn’t mean it’s not there and it’s not causing severe damage. Frozen AC units require immediate attention and service. In more humid climates, it is quite common for air conditioners to begin dripping water. However, if the amount of leaking water in the unit is significant, it is a clear indication of trouble. If your drip pan is filled with water, it unusually means that there is melted ice inside your unit. If you hear falling chunks of ice coming from your AC unit, you probably are in need of professional HVAC repair services. If you are experiencing any of these issues, shut off your air conditioning unit right away and call a qualified HVAC repair technician.

If you live in Middle Tennessee, call FiveStar Plumbing & HVAC at (615) 382-8131 to meet all your heating and cooling needs today!