Why Is My Air Conditioner Freezing Up and How Do I Fix It?

A frozen air conditioner is more than just a frustrating turn of events on a hot summer day. Ice accumulating on your air conditioner’s coils or refrigerant lines can impact the unit’s ability to cool your home efficiently. It can also be a sign of a larger problem and can cause further damage if the underlying issue isn’t resolved.

There are several common reasons for a frozen-up AC. Take a look at some of the causes behind an AC freezing up, ways you can prevent it from happening again, how to fix a frozen AC, and when to call in a professional for an inspection or air conditioner repairs.

Signs of a Frozen-Up AC

Before we get into the causes of a frozen-up AC, you first need to know if your air conditioner is actually frozen. Look for these two signs that your air conditioner has frozen up:

Lack of cool airflow: If little or no air is moving through your vents, ice on the coil may be to blame.
Visible ice on the unit: If you notice frost or ice buildup on the copper refrigerant lines or coils, you’ve got a frozen-up AC. In some cases, an entire block of ice can form on the unit.

If you notice either or both of these signs, read on to learn what causes them and how to fix a frozen air conditioner.

Common Causes of Air Conditioner Freeze-Ups

To understand why your air conditioning is frozen, you should know how it works. The inside of your AC unit consists of a compressor, condenser coil, and a fan. Warm air from inside your home is pulled into the refrigerant and absorbed. The refrigerant is then carried to the outdoor coil and goes through the compressor.

The compressor moves the coolant through the entire system. When the refrigerant transfers through the condenser, the fan distributes air to the condenser coil, which completes the cooling process and blows cold, fresh air throughout your home. But, in some cases, the evaporator coil can get too cold. This can lead to ice forming on the coils or lines that feed it.

A few factors can lead to a frozen AC. Take a look at the four most common reasons your air conditioner is freezing up:

Poor airflow: If your AC isn’t drawing enough warm air from your home to the inside of the unit, there will be nothing to prevent the condensation on the coil from turning into ice. A dirty air filter is usually the main culprit in airflow issues. If changing the filter doesn’t make a difference, inspect your vents and ductwork for visible obstructions.
Low refrigerant: When your air conditioning is low on refrigerant, the coils become too cold and freeze. The most common cause of low coolant is a leak, which requires a significant repair. If your AC is blowing air but the air isn't cold, you likely have low refrigerant and will need to consult with an HVAC professional.
A mechanical issue: A frozen air conditioner could point to a problem with one of its internal components. A broken fan, dirty coils, or many other mechanical issues could be contributing to the freeze. Try turning your system off entirely and allowing it to defrost. If you can't see any mechanical or cleaning issues, contact an HVAC professional.
Broken thermostat: A faulty or broken thermostat is a common cause of a frozen AC. If your unit is only freezing at night, this is a sign that your thermostat isn’t shutting off at the correct temperature, causing the coils to freeze. Try the obvious solution first: Change the batteries. If this doesn’t resolve the issue, you will most likely need a new thermostat.

How to Fix a Frozen AC: Immediate Steps to Take

If you’ve discovered your air conditioner has frozen up, there are a few quick steps you can take to defrost the unit and prevent further damage.

Turn off your air conditioner. First thing’s first: Shut off your cooling system. Otherwise, your air conditioner will continue trying to cool your home, which can lead to more ice building up on your coils or lines.
Turn your fan on. Next, use the fan setting on your thermostat. The fan will circulate warm air through the system and blow it over your coils, which can help defrost the ice. If a substantial amount of ice has accumulated, keep your system on and turn up the heat to help the coils and lines defrost.
Determine the cause of the frozen-up AC. Once you’ve started the defrosting process, determine what caused the problems in the first place. In some cases, it could be that your thermostat was set too low. While every system is different, it’s generally best to set your thermostat no lower than 68° to prevent a freeze-up. If the temperature isn’t to blame, check your air filters and the coils for dust, dirt, buildup, or blockages that could have caused the system to overwork and freeze. Then, inspect your ductwork as well as you can to ensure it hasn’t collapsed. Assess your refrigerant lines for leaks, too.
Call a professional. If you’re not able to determine why your system froze up or you hear a hissing sound coming from the unit, call your local Aire Serv^® for emergency HVAC services. We’ll inspect your unit to determine the problem and provide any necessary repairs to keep it from happening again.

Preventive Measures to Avoid Future Freeze-Ups

Air conditioner freeze-ups are frustrating and can cause damage. Fortunately, there are steps you can take to prevent your AC from freezing up. Take a look at some top maintenance tips to avoid a frozen-up AC unit:

Clean your air filters. Dirty air filters are one of the top causes of a frozen air conditioner. For best results, clean or replace your AC filter once every 1-2 months, especially during periods of high usage.
Check your vents. Check your air vents to make sure they’re not blocked by furniture or other items, which could prevent proper air circulation.
Keep an eye on your thermostat. As mentioned above, setting your thermostat too low—especially on humid days—can be an easy way to freeze up your AC. Aim to maintain a minimum temperature of 68 degrees to reduce the risk of a frozen air conditioner on a hot summer day.
Schedule routine maintenance. Finally, schedule routine maintenance services from an HVAC professional like those at your local Aire Serv. Our team will assess the health of your HVAC unit, check your ductwork, and perform tasks like monitoring refrigerant levels and checking for blockages in the condensate drain, which can help prevent a frozen AC.

When to Seek Professional Assistance

You can usually resolve a frozen AC on your own, but in some instances, you may need professional help. If basic troubleshooting does not resolve the problem or you notice excessive ice buildup or hissing sounds coming from the unit, it’s likely time to call a professional for HVAC repairs.

Keep Your AC Running Smoothly

One of the best ways to prevent your air conditioner from freezing is to have it regularly serviced by the HVAC professionals at Aire Serv. An experienced service professional from your local Aire Serv can help determine the best course of action to keep your AC unfrozen and in excellent condition.

Schedule an appointment online to get started. Have an HVAC emergency? Call for 24/7 customer service and convenient emergency repairs.

This article is intended for general guidance only and may not be applicable to every situation. You are responsible for determining the proper course of action for your property and your situation. Aire Serv is not responsible for any damages that occur as a result of any advice or guidance derived from blog content. For the most accurate guidance, contact an independently owned and operated Aire Serv for more information and a professional on-site assessment.