3 Steps to Fix Your Frozen AC Unit

One of the most common air conditioning malfunctions homeowners face is when their AC unit freezes up. Even though the frosty failure leaves solid ice on your unit, don’t be fooled, the issue will cause your home, and perhaps your temper, to heat up.

Follow this guide to identify why your AC unit is freezing up, and how you can fix it.

What causes an AC unit to freeze up?

Regardless of if you have a window AC unit or a central air conditioner, the reasons behind your AC freezing up are likely the same, as are the solutions for fixing it.

The root cause for your AC freezing up is usually the manipulation of the Joule-Thomson Effect, which is the principle of thermodynamics that allowed us to create an air conditioning unit in the first place.

Stick with us, we won’t get too technical here.

The Joule-Thomspon Effect

The Joule-Thomson Effect is a theory that describes how the flow of gas and pressure work together. In short, the method says that if gas expands, then pressure and temperature will decrease as a result (and vice versa). This is important because your air conditioner works by the evaporator coil expanding refrigerant (the liquid agents that make your AC work) to absorb heat in your home, and then pushing cool air out as a result.

So, your air conditioning unit expands refrigerant and decreases the temperature, sometimes causing it to malfunction, and a frozen AC unit is the result.

The common culprits of a frozen AC unit

Though the process seems complex, the common causes are quite simple.

  • Insufficient air flow: When your air conditioning unit has low airflow the heat in your home can’t be pulled into the unit. When this happens, condensation can form on the coils and turn them into ice.
  • Low refrigerant: Low refrigerant creates low pressure in your AC unit, and as we described above, low pressure equals low temperatures. This can cause your evaporator coils to freeze.
  • Mechanical failures: Air conditioning units are made up of several mechanical components: a fan, compressor, and an expansion device. If any of these components aren’t properly functioning, they can mess with the pressure in your AC unit, which can decrease temperatures in the unit, and cause your air conditioner to freeze up.

How can you fix a frozen AC unit?

When caught early, fixing your frozen AC unit is often a simple solution. Follow the steps below to determine the issue so you can take action.

Step one:  Unthaw your AC unit

If your AC unit is frozen, take steps to unthaw the unit and let the coils dry. To do this, simply switch your thermostat to ‘off’ and your fan to ‘on.’ This will minimize further damage and let you get a better view of what’s happening to your machine.

Step two: Find the underlying cause
  • Check air filters: One of the common causes of blocked airflow in your AC unit is the debris your air filter has caught. As we mentioned earlier, insufficient airflow prevents heat from entering the system and can freeze your unit. If your air filters look dirty, either clean them off or replace the filter if you haven’t done so in a while. Remember, air filters should be replaced every 2 to 3 months.
  • Check coils: If your air filters are clean — or have been recently changed — take a look at your evaporator coil as dirty coils can also impede airflow. Check your AC’s user manual to learn the best way to access your panels and evaporator coils. Then, to clean the coils make sure your AC unit is turned off, and use either compressed air or a soft (not wire) brush to remove debris.
  • Check ductwork: Just like debris can cause airflow issues, so can collapsed ductwork. If ductwork isn’t fitted correctly, it can easily obstruct the flow of air, and therefore block warm air from keeping your unit functioning properly. While some duct issues, like gaps or small holes, can be fixed with duct tape, more extensive damage should be assessed by professionals.
  • Check for leaks: Not only do low levels of refrigerant take away from the functionality of your air conditioning, but it also may indicate a leak. Be sure to check for leaks right away as freon exposure can be harmful after prolonged periods of time. While some refrigerant leaks may be easy to see with the naked eye, slow leaks are more difficult to notice. If your refrigerant levels continue to drop, consider performing a dye detection test to identify slow leaks. A dye leak test is when you place a small amount of fluorescent dye in with the refrigerant. If there is a leak, you’ll notice brighter colors on the ground from the fluorescent dye/refrigerant mixture making it easier to spot.
  • Take a look under the hood: This is where things can start to get more technical. Can you tell if your refrigerant lines are in good shape? Is the blower fan working? Do you have a way to check if your filter dryer is operational? All of these mechanical issues can cause your air conditioner to malfunction, and if you’re a handyperson you may be able to quickly diagnose and replace the parts that aren’t working well. However, if this step is too advanced, it might be time to call in the expert
Step three: Ask for help

If you’re unable to diagnose why your air conditioner is freezing up, or if you notice issues like a leak that requires specialized attention, be sure to consult with an AC professional.

Not only will the pros be able to accurately assess the issues, but they will also be able to provide you an estimate for repairs or help you upgrade to a newer unit, which might be more energy efficient. They’ll help you determine how your return on investment will look over time. This will help you make an informed decision about how to move forward.

How to prevent AC issues before they arise?

It’s also wise for homeowners to schedule professional tune-ups on all heating and cooling equipment in your home to decrease significant issues that could cause you to replace your home appliances prematurely, and also ensures your systems are effectively functioning, which can reduce your bills.

For homeowners in the Fairfield and New Haven Counties in Connecticut, Santa Energy has been a reliable HVAC company for over 75 years. If you have any issues with your air conditioning unit that you’re unable to solve, we’re happy to help.

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