What to Do when an Air Conditioner Freezes

What to Do when an Air Conditioner Freezes
October 15, 2015 nobleair

For most homeowners living in the Valley of the Sun, there will be plenty more days when outside temperatures demand inside air comfort. Residential air conditioning systems are quite remarkable and use clever technology to engage basic physics in order to keep a home cool. One weird phenomenon that some homeowners experience is seeing a large block of ice form on their units. Even though the outside air temperature might be hot, a sheet of ice forms on the system.

What to Do when an Air Conditioner Freezes

When an air conditioner freezes, there’s obviously an explanation for why it happens. In physics, it’s known as the “Joule-Thomson Effect,” or, the “The Joule-Thomson Coefficient.” This states that in a consistent, stable environment, gas expands when pressure decreases, and, gas compresses when pressure increases. Why this is important is it’s a principle that governs how a residential air conditioner unit operates.

The air conditioner’s evaporator coil and condenser coil collect dirt over their months and years of service. A clean filter prevents the evaporator coil from soiling quickly. In time, however, the evaporator coil will still collect dirt. This dirt reduces airflow and insulates the coil, reducing its ability to absorb heat. To avoid this problem, check your evaporator coil every year and clean it as necessary. —U.S. Department of Energy

Your home’s air conditioning unit forces air over a cooled coil, made possible by a fan and refrigerant. It blows this cold air inside, while simultaneously expelling heat outside. When the system isn’t stable, its component operations are forced out of whack. In other words, when an air conditioning unit freezes, it’s because the unit is responding to a change. Unfortunately, it will continue to run, even when such changes occur. When an air conditioner freezes-up, it’s usually do with the evaporator coil, such as insufficient airflow across the evaporator coil, low level of refrigerant, outside air temperature, or mechanical failure. Now, here’s what to do when an air conditioner freezes:

  • Turn your unit completely off. When you notice ice forming on your air conditioner unit, turn the system off immediately. Allowing the unit to continue to run will only worsen the problem, especially if the outside temperature is at 62 degrees or below. The ice will begin to melt but don’t turn the unit back on until you do these other things.
  • Replace the air conditioner filter. Check the air conditioner filter to see if it needs to be replaced. Should it be dirty, replace it immediately with another filter but keep your unit off.
  • Clean the evaporator coil. As the ice melts, you’ll be able to see the evaporator coil. If it appears dirty, then clean the evaporator coil. Be careful when cleaning it to avoid further damage.
  • Check ductwork for any air flow restriction. Next, check the ductwork in the attic. Be sure to only step on joists, and, look for tears in the ductwork, sharp bends, and other things that might restrict or affect airflow.
  • Open registers and look inside. Another thing to check is inside the registers. Use a flashlight to see if there’s anything blocking airflow within.

Now, you can turn your air conditioner back on, but, if the problem persists, you’ll need to have an experienced technician check the system.