Air Conditioners and Icicles Don't Mix

August 03, 2012

Believe it or not, even during the hottest summer on record, ice can from outside…unfortunately, it’s on your air conditioner. Knowing the causes of a frozen air conditioner and when to call a repairman can help keep you from experiencing the wrong kind of cool afternoon breeze.

An air conditioner that accumulates ice and frost most likely has one of these problems:

  • Inadequate or blocked air flow. If your system’s evaporator coil is not getting enough air flowing around it, its temperature will drop below freezing. Then, any humidity in the air settles on the coil and turns into frost or ice.  Causes of inadequate air flow include dirty air filters, ducts that are blocked or undersized, blower motor malfunction, and dirt on the evaporator coil. 
  • Refrigerant issues. The level of refrigerant in your system is critical to its proper operation. If the refrigerant level is not high enough, such as may be the case if there is a leak present, the evaporator coil’s pressure drops enough that any moisture in the air can settle and freeze on the coil.
  • Low outdoor temperature.  We are not too many weeks from overnight temperatures below 60 degrees, even when it’s hot during the day. If an air conditioner is running when the air temperature is below 60 degrees, it can cause the system to freeze. Of course, by the time it cools off to 60 degrees, most of us will turn off our air conditioners, so this is not a common occurrence.

If you notice that your system isn’t cooling properly, check the evaporator coil immediately for any frost or ice buildup. If the ice is left to accumulate it can leak expensive refrigerant as well as cause serious, permanent damage to your system. If you see ice or frost:

  1. Turn off your air conditioner immediately. 
  2. Allow it to completely defrost, about 24 hours.
  3. Clean or replace air filters.
  4. Check for any other visible obstructions or dirt.
  5. Turn your system back on.

If your system does not freeze again, you have solved the problem.  Now, simply remember to keep your filters clean by changing them monthly and keep any other airflow obstructions away from your air conditioner. If, however, your system freezes up again, your problem has not been fixed.  You may have a refrigerant leak or the duct work in your house may be the culprit.  It’s time to call a professional to diagnose and repair your issues. Frozen air conditioners are not a common occurrence, but they can happen if an air conditioner is not maintained correctly. With a few simple precautions, you can keep your air conditioner from freezing and ensure it will keep you cool all year long.


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Last Updated: June 09, 2023