Why Your AC Unit Freezes Up During Summer and How to Prevent It

The Shocking Truth: Why Your AC Unit Freezes Up During Summer and How to Prevent It

It’s the middle of July, temperatures are soaring into the 90s, and you discover your air conditioner has turned into a block of ice. While this might seem impossible, air conditioners freezing up is something that happens a lot during the summer months. Understanding why this occurs and how to prevent it can save you from sweltering heat and costly repairs.

How Does an AC Unit Actually Freeze?

Your air conditioning system works by circulating refrigerant through coils to absorb heat from your home’s air. Airflow, system pressure, and temperature all play major roles in AC performance. When something throws that delicate balance off, refrigerant evaporates at a much lower temperature, and water vapor condenses and freezes on the coil or refrigerant lines.

The result is the air conditioner’s evaporator coil will be unable to properly transfer heat, and in essence ‘overcools’ itself. The net effect of this super-cooling is condensation (that’s water formation), and over time ice forms from that condensation as it cools below the freezing point.

Top Causes of Summer AC Freeze-Ups

Dirty Air Filters

The leading cause of a frozen HVAC system is a dirty air filter. Dirty home air filters block airflow, starving the evaporator coil of the warm return air it needs to stay above 32 °F. This is the single most common reason for HVAC system repair, and it is 100% preventable. When your filter becomes clogged with dust and debris, it reduces the amount of airflow in the system, which can trap the cold air and cause the AC unit to freeze.

Low Refrigerant Levels

Low refrigerant levels are commonly caused by a leak somewhere in your system. Improper refrigerant levels make it hard for your AC unit to regulate the temperature accurately, which then causes your AC to freeze. A refrigerant leak results in low refrigerant levels/low charge which means your cooling system can’t run as efficiently as it should. If you notice an oily residue around your indoor coil or a hissing sound near the indoor coil or outdoor condenser coil, call an HVAC professional right away.

Blocked Vents and Poor Airflow

Ensuring your vents are open and free of any potential blockers like furniture is an easy way to prevent your AC system from freezing. Blocked or closed vents can lead to airflow issues, which then leads to your AC system freezing. Blocked or closed vents prevent warm air from properly circulating through your AC system. With limited airflow, the evaporator coil can’t absorb enough heat—causing it to get too cold and possibly freeze.

Malfunctioning Blower Fan

Your AC system’s blower fan generates the airflow needed to keep the evaporator coil from freezing. A low-functioning or broken fan will severely impact the system’s airflow and can lead to the system freezing up.

Cool Nighttime Temperatures

Air conditioners are calibrated to operate within a certain set of optimum temperature thresholds. When nights in the summer time are colder than the optimum threshold can account for, it can throw an AC out of whack. A good rule to remember is that when the outdoor air temperatures dip, you should turn your air conditioner off. Icing can occur if you run your unit on cooler nights.

What to Do If Your AC Freezes

If you discover ice on your AC unit, You SHOULD NOT DO THIS. IT MAY CAUSE IRREPARABLE HARM TO YOUR COOLING SYSTEM. If you have frozen coils, the first thing to do is turn your AC or HP unit off and allow the coil to defrost. Go to your thermostat and switch it from Cool to Off.

Next, Switch the fan to ON (instead of AUTO). Moving indoor air helps the coil thaw faster. Replace the air filter with a new, correctly sized filter. Wait until all ice is gone before restarting cooling mode. Starting too soon can slug liquid refrigerant into the compressor.

Prevention is Key

The best approach to avoiding AC freeze-ups is regular maintenance. With proper maintenance, such as cleaning or changing the air filter and scheduling professional HVAC maintenance each spring, you can largely avoid frozen coils in the future.

Here are essential prevention steps:

When to Call a Professional

If the unit freezes again within 24 hours, you likely have a refrigerant or blower issue that requires professional tools. Issues involving refrigerant leaks, electrical problems, or mechanical failures require the expertise of licensed HVAC technicians.

For residents in New Jersey dealing with AC freeze-ups, professional AC Repair in Montclair NJ services can quickly diagnose and resolve these issues. This can become a pricey repair. When your AC ices over it can lead to damage to the compressor. Replacing your compressor could easily cost as much as a down payment on a high efficiency model.

Don’t let a frozen AC unit leave you sweating through the summer. By understanding these common causes and taking preventive measures, you can keep your cooling system running efficiently all season long. Remember, when in doubt, it’s always better to call a professional than risk causing expensive damage to your system.