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Why is Ice Forming on the Inside of My Air Conditioning (AC) Unit?

Why is Ice Forming on the Inside of My Air Conditioning (AC) Unit?

You’re concerned. Your central air conditioning isn’t cooling your home very well. So you go to check your equipment and discover ice on the inside unit of your air conditioning (AC) system. You may find this issue strange considering it’s summer.

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What Causes an Air Conditioner (AC) to Freeze Up Inside?

What could be the problem? There are 2 main issues causing this. Read on to learn what they are and what to do about them or reach out to a professional to receive assistance with the issue.

1) Weak & Reduced Airflow Over the Evaporator Coil

Reduced airflow to the inside unit will cause the refrigerant coil to freeze up. First, we will tell you what usually causes reduced airflow to the inside unit and then explain the science behind why reduced airflow would cause ice to form on your AC unit.

What to Do:

  • Change the air filter: A dirty air filter blocks air from returning to the inside unit.
  • Unblock return grills: Move curtains or furniture blocking return vents that block air from returning to the inside unit.
  • Open closed supply vents in unused rooms: Closing supply vents in unused rooms does not save you money. It causes several problems instead, like a frozen inside unit.
  • Have a professional look at the blower: The coil will freeze if the motor in the blower malfunctions in the inside unit of the air conditioning (AC) system and isn’t pulling in enough air.
  • Have a professional clean the evaporator coil: Dirt insulates coils from heat, meaning that they can’t absorb heat from the air being pulled over it by the blower motor.

OK so those are some “to-dos”. But why do you need to do them?

Why is Ice Forming on My Inside Air Conditioning (AC) Unit?

Why Restricted Airflow Causes the Coils to Freeze Up

The evaporator coil, tubes forming the A-shaped part of the inside unit, has cold refrigerant flowing through it. A blower pulls in air from your home and over that coil, cooling the air in your living space.

However, when there is little to no air flowing over the cold evaporator coils, your air conditioning (AC) unit will freeze up and excess ice will form on the coils. When it’s frosted over, air can’t easily flow through the coils because it’s a solid block of ice, reducing airflow to your home.

Here’s an illustration: Imagine you have a cup of water and every hour you add 5 ice cubes into it. You also have a hair dryer blowing hot air over the cup. Obviously, the ice would melt after you add ice into the cup.

Now imagine that you put something in between the hair dryer and the cup while you’re still adding ice to the cup. Since there’s something blocking airflow to the cup, the ice isn’t melting. This would continue until the cup is completely full of ice. That’s basically what’s happened to the inside unit. Follow our instructions from before to make sure there’s enough airflow going over the coils!

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2) Low Refrigerant

This is the most common cause of a frozen evaporator coil. When your AC system is low on refrigerant, the pressure drops causing the evaporator coil to get abnormally cold.

So when returning air hits the coil, humidity/moisture from the air beads ups on the coil and quickly freezes. This continues until the evaporator coil is frozen. If you’re low on refrigerant you also have a refrigerant leak. That means you will need a professional to find the leak and fix it before adding more refrigerant.

Worst-case scenario: The leak can’t be fixed and one of the refrigerant coils needs replacing. This is an expensive air conditioning replacement. So if your AC unit is 15+ years old, you should consider replacing it.

What You Can Do ASAP:

  1. Turn off your air conditioner
  2. Let the AC defrost
  3. Change your air filter (If it’s dirty)
  4. Open all the closed supply vents in your home
  5. Ensure no furniture or drapes are blocking the return vents

If the inside unit of your air conditioning (AC) system continues to freeze up after you have replaced the air filter and adjusted your vents, you will need to call a professional to resolve the issue.

Air Conditioning Repair and Installation Services

Air Conditioning Repair & Installation Services

When you are having problems with your air conditioning system, you can book an appointment with our professional technicians to receive assistance. Our team provides exceptional air conditioning repair and installation services for homeowners in Framingham, MA and other areas. In addition, we provide other types of HVAC services such as furnace replacement, boiler maintenance, air conditioning installation, and furnace repair. Give our team a call by phone at (508) 301-1767 to receive help with a malfunctioning air conditioning system.