Frozen AC Unit

Why Does My AC Keep Freezing Up?

An air conditioner that keeps freezing up can be a frustrating issue, especially during the hot summer months when you need it the most. Understanding the reasons behind a frozen AC coil can help you address the problem effectively and ensure your home stays cool and comfortable. In this blog post, we’ll explore the common causes of AC freeze-ups and provide tips on how to prevent them.

What Causes AC Coils to Freeze?

There are several reasons why your air conditioner’s coils might freeze. Here are the most common causes:

1. Restricted Airflow

One of the primary reasons for a frozen AC coil is restricted airflow. When the airflow over the evaporator coil is insufficient, the coil can get too cold and freeze up. This can happen due to dirty air filters, blocked vents, or issues with the blower fan.

2. Low Refrigerant Levels

Refrigerant is essential for the cooling process. If your AC has low refrigerant levels, it can cause the evaporator coil to freeze. Low refrigerant levels are often a result of a leak in the system, which requires immediate attention from a professional technician.

3. Thermostat Issues

A malfunctioning thermostat can cause your AC to run continuously, leading to a frozen coil. If the thermostat doesn’t signal the system to cycle off, the evaporator coil can become excessively cold and freeze.

4. Dirty Coils

Dirt and debris on the evaporator coil can restrict heat absorption, leading to a frozen coil. Regular maintenance, including cleaning the coils, can prevent this issue.

5. Drainage Problems

If the condensate drain is clogged, water can back up and freeze on the evaporator coil. Ensuring that the drainage system is clear and functioning properly can help prevent freeze-ups.

Why Does My AC Keep Freezing Up?

Now that we’ve covered the common causes, let’s dive deeper into why your AC might keep freezing up repeatedly.

1. Inadequate Maintenance

Regular maintenance is crucial for the optimal performance of your air conditioner. Without it, small issues can escalate, causing your AC to freeze up. Scheduling routine check-ups with a professional HVAC technician can help identify and fix potential problems before they lead to a freeze-up.

2. Environmental Factors

Certain environmental conditions can contribute to your AC freezing up. High humidity levels, for instance, can cause excessive condensation on the evaporator coil, leading to freezing. Additionally, running your AC when the outdoor temperature is too low can also cause the system to freeze.

3. Incorrect Thermostat Settings

Setting your thermostat too low can cause the evaporator coil to freeze. Ensure that your thermostat is set to a reasonable temperature, typically between 72-78 degrees Fahrenheit, to prevent this issue.

4. Oversized AC Unit

An oversized AC unit can cool your home too quickly, leading to short cycling. Short cycling prevents the system from running long enough to dehumidify the air, which can cause the evaporator coil to freeze. If you suspect your AC unit is oversized, consult with an HVAC professional for a proper evaluation.

How to Prevent Your AC from Freezing Up

Preventing your AC from freezing up involves regular maintenance and a few simple steps to ensure proper operation. Here are some tips:

  • Change the Air Filter Regularly: A clean air filter promotes good airflow, which is essential for preventing frozen coils. Check and replace your air filter every 1-3 months, or as recommended by the manufacturer.
  • Schedule Regular Maintenance: Having your AC system inspected and maintained by a professional at least once a year can help identify and fix issues before they lead to a freeze-up. Maintenance tasks include cleaning the coils, checking refrigerant levels, and ensuring proper drainage.
  • Keep Vents and Registers Clear: Ensure that all vents and registers in your home are open and unobstructed. Blocked vents can restrict airflow, causing the evaporator coil to freeze.
  • Monitor Refrigerant Levels: Low refrigerant levels can cause freeze-ups and indicate a leak in the system. If you suspect a refrigerant issue, contact a professional HVAC technician to check and refill the refrigerant as needed.
  • Adjust Thermostat Settings: Avoid setting your thermostat too low. Keeping it at a reasonable temperature will prevent the evaporator coil from becoming excessively cold.
  • Address Drainage Issues: Ensure that the condensate drain is clear and functioning properly. A clogged drain can cause water to back up and freeze on the evaporator coil.
  • Use a Programmable Thermostat: A programmable thermostat can help regulate your home’s temperature more effectively, preventing the AC from running continuously and reducing the risk of freeze-ups.

Why Does My AC Freeze Up at Night?

It’s not uncommon for homeowners to notice their AC freezes up at night. This can happen due to lower outdoor temperatures, which can cause the refrigerant pressure to drop and the evaporator coil to freeze. Additionally, nighttime humidity levels can rise, leading to increased condensation and potential freeze-ups. To mitigate this issue, consider the following:

  • Increase the Thermostat Setting: Raising the thermostat temperature by a few degrees at night can help prevent the coil from freezing.
  • Use a Fan: Running a fan can help circulate air and reduce humidity levels in your home.
  • Schedule Nighttime Maintenance: If the problem persists, consider scheduling a maintenance check with a professional technician to identify and address any underlying issues.


Dealing with a frozen AC coil can be frustrating, but understanding the causes and taking preventive measures can help keep your air conditioner running smoothly. Regular maintenance, proper thermostat settings, and ensuring good airflow are key to preventing freeze-ups. If you’re experiencing recurring issues with your AC freezing up, it’s essential to consult with a professional HVAC technician for a thorough inspection and repair.

At Ultimate Heating & Air, we offer comprehensive HVAC and plumbing services to keep your home comfortable year-round. Contact us today for expert solutions to all your heating, cooling, and plumbing needs. Don’t let a frozen AC coil ruin your summer—trust the professionals at Ultimate Heating & Air to keep your system in top shape.


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