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Why Do Air Conditioners Freeze Up?

It seems to defy logic. The temperatures outdoors are in the 90s or 100s. Yet, your air conditioner isn’t working right because it’s…frozen?

Not only is this possible, it’s a common issue when A/C units are working overtime in the heat of summer and autumn.

There is a thermodynamic name for why A/C units freeze up, called the Joule-Thomson Effect. Rather than going into that right now, let’s discuss what you’re probably here to find out: the causes of air conditioner freeze-up, how to prevent it, and how to get your frozen air conditioner blowing cool air again.

Important Note: If your air conditioner is frozen, don’t run it. Not only will it not cool your home, it could damage the compressor—a costly repair! Turn the air conditioner off.

4 Common Reasons Air Conditioners Freeze Up and What You Can Do

There are multiple possible causes for air conditioner freeze-up. Some are simple and some are complex. What they all have in common is that the A/C unit is working overtime and not getting the help it needs to function properly.

Potential Cause #1: Dirty Air Filter

Restricted air flow due to a dirty air filter can contribute to air conditioning freeze. This is easy to fix and even easier to prevent. We recommend checking your air filter every month and changing it if it’s dirty. Not sure? Hold the filter up to the light. If you can’t see through it, it needs to be changed. Often this works out to a filter change every 60 days, or 90 at the maximum. If you have pets in the home or excessive dust, you may need to change your filter every 30 days.

If your air conditioner is frozen and the filter is dirty:

  1. Turn off power to the A/C unit and allow it to thaw.
  2. Replace the filter and turn on the fan only for a minute or two. You can then repower the A/C unit.
  3. If cooling is restored, your problem is solved!

Potential Cause #2: Problem With the Blower Motor or Relay

A blower motor can overheat and stop working intermittently or altogether. A relay may stick or malfunction causing the motor to not operate properly. These are issues that need to be traced through HVAC troubleshooting performed by an HVAC professional.

Potential Cause #3: Dirty Evaporator Coil

Like air filters, evaporator coils (located in the interior unit of the A/C system) can get dirty over time. As the dirt on the coil increases, your A/C unit becomes less and less efficient, often leading to your air conditioner freezing. Unlike an air filter, a dirty evaporator coil is best corrected by a professional.

Potential Cause #4: Leaking Refrigerant

A lack of refrigerant is one of the leading causes of air conditioner freeze-up. This can be due to even a tiny leak.

Having an HVAC professional refill your system may solve the problem—but it may only solve it for hours, days or weeks. A trusted technician can determine the extent of the leak through HVAC troubleshooting and give you options including necessary repairs. Depending on the age of your unit, replacement may be the best option.

Regular Maintenance Is the Best Way to Prevent Air Conditioner Freezing

A thorough A/C tune-up and cleaning once a year is the best way to prevent your air conditioner freezing up on you when you need it most. For example, Althoff’s 24-point A/C Tune-Up includes testing the blower motor and checking the refrigerant. While there’s no way to predict absolutely everything that could happen during the year (especially on an older unit), it’s the absolute best way to catch potential issues and get your A/C running at its best before the blazing hot weather arrives.

Air Conditioner Frozen? You Need an HVAC Technician You Can Trust

Some of the causes of a frozen air conditioner we covered above are routine and can be resolved with minimal cost. Others are terminal and may result in system replacement. The guidance of a trusted HVAC professional is critical in these circumstances.

If you’re in the Chicago area and experiencing air conditioner freeze-up (or any A/C problem), the experts at Althoff Industries can help. We’re a family-owned and operated company who has been helping Chicagoans stay cool for nearly 60 years. Request service online or give us a call at (815) 455-7000. 24/7 emergency service available.

This information is provided as a general guideline. Althoff Industries does not assume any liability resulting from the provided information.

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