Having an AC unit that’s cold is good, but if it’s frozen, things have gone too far. AC units that freeze-up is less efficient, consume more electricity, and can lead to water damage in your walls and ceiling if left unattended. A unit might be prone to freezing for several reasons and can be an easy repair if caught early. Acting fast is important–waiting too long can mean paying more for a fix or having to replace the entire unit.

There are three common reasons why AC units freeze:
  • Low refrigerant – It might sound a bit backward, but having too little refrigerant in the system can lead to your AC freezing up. This is because the less refrigerant you have in your air conditioner, the cooler that liquid must be to evaporate. This causes the entire unit to over-compensate and drops the temperature below safe design standards. The moisture found in the AC unit then freezes and stops the whole system. Generally, low refrigerant means you have a leak. Finding and repairing the leak will solve the freezing problem, but since it may require the addition of extra refrigerant to the system it’s best left to a professional.
  • Poor airflow in the AC system – The AC unit relies on having a steady amount of air running through the unit to work correctly. If this airflow is blocked by something, the colder air stays in the AC for longer and ice forms in the unit. Many parts of the system can restrict airflow including:
    • Air filters – These filters block particles in the air from entering the unit and going into the evaporator fins. Depending on where you live and how much dust is in your household, these filters need to be cleaned or replaced on a regular basis. They clog up with dust and dirt fast and lower the effectiveness of the unit. Replacing them is part of any regular AC tune-up.
    • Fan or blower – These are the parts of the AC unit that move the air around and out of the unit. If a fan burns out or the connections get corroded, the air stops moving out of the unit and causes a freeze up.
    • Evaporator coil – These are the workhorses of the AC unit and they can also get clogged up with dirt and dust especially if the air filters are already dirty.
  • Low outside temperature – AC units have optimal temperatures when they work best and tend not to do well when below those levels. If you run your AC when it’s cold outside, the pressure in the unit drops and it freezes up. If you’re running your AC during the day, make sure to turn it off for the night if it’s going to get chilly. If you still want fresh air, you can always use the blower function to bring outside air indoors.

AC units need constant maintenance and care to work at their best. A unit freezing is a sign something has gone wrong and that it’s probably time to either repair or tune up your system. Regardless of what reason your AC unit is freezing, make sure that you get it looked at right away–because neglecting the problem will just lead to bigger, more expensive issues in the future.

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