Frozen AC Coils – It's Probably Not What You Think!

Posted on: 8 November 2022


If you have an older or poorly maintained air conditioning system, you may have noticed your evaporator coils freezing up when you push the system a little bit too hard. Your evaporator coils sit at one end of the refrigerant cycle, and their job is to transfer heat from your home into the refrigerant. As a result, the coils can become fairly cold relative to the surrounding air.

Since the coils are cold, moisture will condense onto them, which is why your air conditioning system can dehumidify the air. If the coils become too cold, that moisture will freeze and cause your system to stop working temporarily. However, this isn't usually due to the system working too hard or outdoor temperatures being too high.

How Air Conditioning Coils Freeze

It's easy to think of the refrigerant in your air conditioning system as similar to fluids in other contexts, such as a car's cooling system. If your car runs low on coolant, you can expect the engine to overheat rapidly. You might think that your air conditioning system would work similarly – as the coolant pressure decreases, the temperature in your home will go up.

In reality, there's a much less intuitive relationship between refrigerant pressure and temperature. As the refrigerant pressure in your evaporator coil falls, the temperature at the coil will also drop. Manufacturers design their systems to produce a certain temperature (always above freezing) in the coil, ultimately providing the cool air that will blow through your home.

Maintaining this ideal temperature also means maintaining the ideal refrigerant pressure. Leaks that allow refrigerant to escape or restrictions that reduce pressure can affect the temperature at the evaporator coil. Low temperatures lead to ice formation, which creates an insulating barrier around the coil that will stop it from absorbing heat and cause your system to stop working.

Why Refrigerant Pressure Drops

It's a common misconception that overworking an air conditioner will cause it to freeze. This misconception exists because the longer an air conditioner runs, the more time ice will have to form and insulate the coil. However, a well-maintained air conditioner with good airflow and proper refrigerant pressure will not freeze, even if you run it all day.

Instead, a frozen evaporator coil nearly always indicates an underlying problem with system airflow, refrigerant pressure, or refrigerant flow. Common underlying causes include dirty airflows, blocked return vents, refrigerant leaks, and even refrigerant restrictions. These problems require attention and can cause further damage to your system if you ignore them.

If you experience frequent freezes with your air conditioning system, it's not simply an issue of your system becoming old or working too hard. These problems always mean that there's an issue you need to address, and repairing the underlying cause will get your system working correctly again while also protecting it against more severe damage.

For more information, reach out to an AC repair service near you.