Pressure gauges and hardhat on HVAC compressor

Has your AC or heat pump ever mysteriously stopped working over the summer? Believe it or not, a cause of the slow trickle of cold air could be that your unit has frozen. As the sweltering heat outside battles the bracing cold within your home’s walls, the clash often leads to an icy buildup in your air conditioning unit. In this blog, we’ll defrost the secrets behind this dilemma and arm you with the knowledge to keep your cool all summer long. Need help with your cooling this summer? Call Mode Comfort to make an appointment!

What happens when your AC freezes up?

When your AC system freezes up, it’s crucial to understand the potential reasons behind this common problem. Typically, a frozen air conditioner or heat pump can indicate an airflow issue, such as dirty air filters or blocked vents, which prevent your system from functioning efficiently. Another possible cause is low refrigerant levels, which can occur due to leaks or insufficient charge, causing the evaporator coils to get too cold and ice over. A frozen AC not only reduces cooling performance but can also lead to more severe damage if not addressed promptly. By taking quick action and performing routine maintenance, you can extend the life of your air conditioning unit or heat pump and ensure it operates at peak efficiency during those sweltering summer months. Find out about our HVAC repair services!

Signs of AC Freeze Up

  • Ice on the evaporator coils: When your air conditioner or heat pump begins to freeze up, you might notice a buildup of frost or ice on the evaporator coils, which are located inside the air handler.
  • Visible frost on the refrigerant lines: The lines that carry refrigerant may also show signs of frost or ice, indicating that the AC unit is operating below its normal temperature range. This could be a sign of the AC lines freezing.
  • Reduced airflow from vents: If there’s a blockage caused by ice, you may experience a significant decrease in air flowing out of your home’s vents, making the AC less effective at cooling your space.
  • Water leaks around the AC unit: Melting ice can lead to water pooling around the air conditioner or heat pump, which is not only a sign of a freeze-up but can also cause water damage to your home. Please note that high humidity may also cause your unit to sweat.
  • Unusually high utility bills: A frozen AC unit has to work harder to cool your home, which can lead to an unexpected increase in your energy costs.
  • Blower fan running continuously: The blower fan might continue to run as it tries to push air through the blocked system, and this constant operation can be a sign that the system is frozen.
  • System cycling on and off frequently: Short cycling, or the system turning on and off repeatedly over a short period, can indicate that the AC or heat pump is having trouble maintaining the desired temperature due to a freeze-up.

Common Causes of an AC Freeze Up

Close-up of HVAC internal wiring

  • Low refrigerant levels: When the refrigerant in your AC unit is low, it can cause the pressure in the system to drop, leading to the evaporator coil freezing over.
  • Insufficient air flow: If the air flow across the evaporator coil is restricted due to a dirty air filter or blocked air ducts, the coil may not be able to transfer heat effectively, causing it to freeze.
  • Dirty evaporator coils: Over time, coils can become coated with dust and debris, insulating the coil and preventing it from absorbing heat from the air, leading to a freeze-up.
  • Faulty blower fan: The blower fan helps circulate air over the evaporator coil. If it is malfunctioning, air won’t move as it should, potentially causing the coil to freeze.
  • Collapsed ductwork: Crushed or collapsed air ducts can significantly restrict airflow, increasing the likelihood of the evaporator coil freezing.
  • Closed supply registers: If too many supply registers are closed, it can reduce the airflow to the evaporator coil, contributing to the freezing problem.
  • Running AC when it’s too cold outside: Using the AC when outdoor temperatures are too low can cause the refrigerant to run cooler than designed, potentially leading to frozen coils.
  • Thermostat issues: If the thermostat is malfunctioning, it might cause the AC unit to run longer than necessary and cool to the point where the coils freeze.
  • Drainage problems: If the drain pan or drain line is blocked, water can back up and freeze on the coil, especially when it’s combined with other factors like low airflow or dirty coils.

How to Fix a Frozen Unit

  1. Turn Off Your HVAC System: This may seem obvious, but it’s a vital first step. Continuing to run a frozen system can cause more harm. Switch the unit off at the thermostat and at the breaker if necessary.
  2. Allow the Unit to Thaw: Depending on the extent of the AC freeze up, this might take a few hours or even a full day. Place towels around the unit to absorb any meltwater. If your unit is indoors, consider using buckets and make sure to monitor the situation to prevent any water damage.
  3. Inspect Air Filters: While you wait for the unit to thaw, check your air filters. Dirty filters restrict airflow and can cause the system to freeze. If they’re dirty, replace them.

Further Diagnostic and Fixes

  1. Check Vents: Ensure all supply and return vents are open and free of obstructions. Blocked vents can lead to a buildup of cold air and moisture in the system. 
  2. Inspect the Blower Fan: After thawing, but before turning the unit back on, check if the blower fan is working correctly. A broken or malfunctioning fan can’t circulate air, leading to freezing.
  3. Look at the Evaporator Coils: If your filters are clean and vents unblocked, the problem might lie with the coils. If there’s dirt on these coils, clean them carefully. Be gentle to avoid damaging the fins.
  4. Examine the Refrigerant Levels: Low refrigerant levels can reduce pressure in the system, leading to an air conditioning unit freezing up. This fix usually requires a certified technician, as it involves handling potentially hazardous materials and checking for leaks.

How Do I Keep My Air Conditioner From Freezing Up?

A family enjoying time together in a living room.

To prevent future freeze-ups, regularly change your air filters, schedule annual maintenance checks with a certified HVAC technician, and ensure proper insulation and sealing of your home to keep the air temperature around the unit as stable as possible. Blocked or restricted airflow can cause the unit to work harder, leading to an overworked system and potential AC freeze up. So, keep your vents open and unobstructed to promote efficient operation. Furthermore, pay attention to the coolant levels—low refrigerant could be a culprit in reducing your AC’s efficiency and causing it to freeze. Also, during hot summer months, avoid setting your thermostat too low, as overcooling can also cause freezing issues. Stick to recommended temperature settings and consider using a programmable thermostat to optimize your home’s cooling schedule. Remember, preventing AC freeze-ups not only extends the life of your unit but also keeps your energy costs in check, making it an eco-friendly and cost-effective practice. Keep these tips in mind, and enjoy a cool, comfortable home without the dreaded freeze-up.


How long should I leave my AC off if frozen?

As a general rule of thumb, it is safe to leave your frozen AC unit switched off for at least 24 hours. This time frame should be sufficient for the ice to fully melt in most conditions. Please note that larger units suffering from AC freeze up with a significant amount of ice may require more time, potentially up to 48 hours.

Why is my brand new AC unit freezing up?

One of the most common causes for an AC unit or heat pump to start freezing is insufficient airflow. Your AC unit’s evaporator coils need a steady stream of air to absorb heat effectively. If the airflow is restricted, the temperature of the coils can drop too low, leading to the condensation on them freezing over. If you are having problems with your new AC or heat pump, learn more about Mode’s AC installation and repair services.

When should I call a professional for an AC freeze up?

If you’ve completed these steps and your unit continues to freeze, or you’re not comfortable performing any of these tasks, it’s time to call a professional. Mode Comfort’s technicians have the tools and expertise to diagnose complex issues and perform safe repairs.