AC Frozen? Here’s How to Fix It

By Kelly Boyer Sagert | Advertiser Disclosure

Your air conditioning unit can freeze if the refrigerant inside the system falls below 32°F. When there’s too much strain on a frozen air conditioner, the compressor can become damaged, which can destroy the entire appliance. Not to mention, a frozen air conditioning system is less efficient and can’t cool your home effectively.

If you notice that your AC is frozen, address the issue as soon as possible to prevent a bigger problem from arising. Keep reading to learn why an AC freezes, signs that indicate your unit is frozen, how to troubleshoot the issue, and when to call in a professional.

What causes an AC unit to freeze?

Air conditioners freeze for a variety of reasons, including:

  • Registers are closed
  • Drain pipes are blocked 
  • The thermostat is no longer working
  • The system is overworked, which can happen if the unit is too small for the job it’s expected to do
  • Dust, dirt, and debris has built up, restricting air flow over the evaporator coils
  • There’s a leak in the refrigerant line or the system is low on refrigerant
  • The system’s expansion valve is stuck
  • A damaged part, such as a broken blower fan, or mechanical failure is preventing the system from working properly
  • Ductwork has collapsed (this may indicate that ducts are undersized)
  • There’s too much humidity in the air

How to tell if your AC is frozen

If you’re wondering how to tell if your AC is frozen, here are a few signs you should look out for:

  • Ice on the evaporator coil
  • Warm air blowing from the system
  • Evidence of a leak in the refrigerant line

Troubleshooting a frozen AC unit

After assessing that your AC is frozen, put towels around the unit to prevent melted ice from flowing over the drain pan and creating slippery conditions around the air conditioner. Then, follow this step-by-step guide to address the issue:

  1. Shut off the air conditioning system at the electrical breaker. Note: it’s not enough to turn up the thermostat to stop the unit from running—make sure the entire system is off.
  2. Ensure that the air registers and cold air returns are open and aren’t blocked by an object, like a rug or curtain. If the registers are closed or blocked, open them and remove any obstructions.
  3. Check the air filter in your HVAC system and replace the filter if you notice a build-up of dirt and debris. This should take less than 10 minutes to complete.
  4. If you don’t have enough air flowing over your evaporator coil, it can freeze. If you have a frozen evaporator coil in your system, use a blow dryer to melt the ice or turn the air conditioning fan on to blow warm air over the frozen coils (this should be done with the AC system in its “off” position). Don’t try to manually brush off the ice because this could damage the coils.
  5. Clean dirty coils with a brush and a commercial coil cleaning product. Let them dry before turning on the HVAC system.
  6. Check your ductwork to see if there are any blockages. Extremely dirty ductwork could cause a blockage.
  7. If you have a clogged condensate drain, which can be diagnosed by evidence of dripping water, mold, or water damage, it’s a good idea to call a local HVAC professional to fix the problem. Your HVAC is one of the most used systems in your home, so it makes sense to let a professional tackle the toughest jobs.

Note: Don’t top off coolant levels as part of your ongoing maintenance or during troubleshooting. Each air conditioning system has an optimal amount of refrigerant, called its charge, that lasts for its full service life. If you assume your system has low refrigerant levels and add more refrigerant, this could cause your compressor to break down.

The only time refrigerant would need to be added to your AC system is if you have a leak. You might have a refrigerant leak if you notice ice starting to develop around the evaporator coil, you hear a hissing sound coming from the system, or there are hot spots in rooms that used to be cool.

Whatever you do, don’t try to seal the leaks with caulk, as this could cause a blockage and create more damage. If you have a refrigerant leak, call a professional to add more to your system.

If these troubleshooting steps don’t fix your air conditioner, you may need to call a local HVAC professional to repair or replace the system. An HVAC professional can help you choose the right system and help you secure a model from manufacturers at a lower cost. After purchasing your new unit, compare HVAC warranties to ensure you’re protected in the event of a repair or costly replacement.

How to prevent your air conditioner from freezing

To help prevent your air conditioning system from freezing, create a preventative maintenance plan and schedule system maintenance at least twice a year (we recommend performing maintenance in the spring and fall). This will help:

  • Keep your entire system clean
  • Ensure that condensate drains are functioning properly and free of debris
  • Improve indoor air quality
  • Keep refrigerant levels at the appropriate levels; if levels are low, leaks can be identified and fixed before they get larger
  • Verify that the thermostat is operating correctly
  • Prevent the need for larger AC repairs or a complete system replacement

In between HVAC service visits, you should always remember to:

  • Change dirty air filters at least twice a year
  • Clean evaporator coils with a brush and coil cleaner
  • Keep debris away from the inside unit
  • Trim tree branches and bushes, keeping debris away from the outside unit

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