What to Do When Ice Forms on Your Air Conditioning Unit


Ice forming on your air conditioning unit? Here's what to do.

If there's one air conditioning problem that leaves more homeowners scratching their heads and wondering what to do than others, it's ice forming on or inside of AC units. The reason this phenomenon is so confusing to most people is that it typically occurs on the hottest days of summer.

Why AC Units Freeze in the Middle of Summer

Before calling for AC repair, there are a few steps you can take to try resolving the problem at home. The first of them is to understand how this unusual phenomenon occurs, which requires having at least a basic idea of how modern air conditioners work. Here's what you need to know:

  1. Air conditioners circulate their refrigerant through outdoor units to condense it from a gas into a liquid, which is then forced through their evaporator coils.
  2. Air is circulated through those evaporators with a fan, cooling down as it comes into contact with the coils.
  3. Contact with the warm air turns the refrigerant back into vapor as heat is removed, at which point the cooled air is sent back into homes.
  4. The condensers turn the vapor back into liquid, removing the heat and beginning the process all over.

When the temperature in your AC unit's evaporator coils falls below freezing, that's when ice begins to form. As you likely already know from experience, that ice buildup significantly reduces your AC unit's efficiency and can even make it impossible for the unit to effectively cool your home.

Causes of Ice Formation

Now that you understand where and how the ice forms, it's time to discuss explanations for why it's happening so that you can figure out what to do. There are three primary reasons that ice might form on an air conditioner's evaporator coils, each of which requires a different resolution.

1. Reduced Airflow

The most common reason for evaporator coils to freeze up is reduced airflow. If too little air is flowing over the coils, excessive ice forms as cold builds up thanks to the refrigerant but can't be transferred to the air. This, in turn, causes further airflow issues as the coils frost over, creating a negative feedback loop that culminates in uncomfortably high indoor air temperatures. Potential underlying causes of reduced airflow include:

  • Dirty evaporator coils
  • Dirty air filters
  • Closed vents
  • Damaged ductwork
  • Damaged or defective blower fan

2. Low Refrigerant Temperature

Evaporator coils are filled with refrigerant intended to absorb the heat coming from the untreated air inside your home, but that doesn't mean colder is better. In fact, if the temperature of your air conditioner's evaporator coils gets too low, it causes a pressure drop. This, in turn, raises the relative humidity level and creates problems with condensation when the hot air hits the coils' surface, causing the moisture in the air to bead up and freeze. Common causes of low coil temperatures include:

  • Low refrigerant levels
  • Refrigerant leaks
  • Excessively cold outdoor temperatures
  • Mechanical failures leading to low pressure
  • Kinks in the refrigerant line

3. Clogged Condensate Drain Pipe

The condensation issues described above occur when hot air hits excessively cold evaporator coils. However, some amount of condensation is normal. Under proper operational conditions, the condensation remains warm enough to avoid freezing, then drips into the drain pan and gets routed out of the system via its drain pipe. If that pipe gets clogged, the condensation continues to build up on and around the coils, increasing the chances that they will freeze.

What to Do About Frozen Coils

Regardless of what is causing your air conditioner's evaporator coils to freeze, the first step towards resolving the problem is always the same. You should turn the air conditioner off and allow the coils to thaw. This can take up to 24 hours, depending on how much ice has already built up. You can also speed up the thawing process by setting your AC unit to "fan only," which allows the fan to move warm air across the iced-over coils. Just be sure to have something available to catch the melting water, especially if you're concerned about the potential for a clogged drain pipe.

Troubleshooting Reduced Air Flow

You don't have to wait until the system is completely thawed to start troubleshooting. In many cases, the primary factor driving coil freezing is a dirty, clogged air filter. All you have to do to resolve this problem is install a new one, then wait for the system to finish thawing before turning it back on. While you're waiting, you can also check around the home to make sure that none of the vents are blocked and that the ductwork hasn't sustained any visible damage.

When the ice has melted, and the system has returned to its ambient temperature, try turning it back on. If a dirty filter or blocked vents were to blame, it should operate as usual. Otherwise, that means there's something else wrong that will require professional help.

Identifying Refrigerant Issues

Some types of refrigerant issues are easy to detect. Leaks in the system, for instance, are typically accompanied by not just iced-over coils but also hissing or gurgling sounds coming from the indoor unit. If you believe there may be a refrigerant leak, call an HVAC technician right away. Refrigerant poisoning can cause serious health concerns and can be fatal if left untreated. 

If kinks in the refrigerant line or mechanical failures are causing excessive cooling of the evaporator coils, you won't be able to diagnose or troubleshoot the problem alone. Give us a call to schedule a full inspection and repairs.

Warm Up Your AC to Cool Down Your Home

No matter why your air conditioner is developing ice, we can help you resolve the problem so that you can go back to efficiently cooling your home. There's no AC issue we haven't seen. Regardless of what's causing your ice buildup, our team of expert HVAC technicians can help. Reach out to schedule an appointment today by filling out a contact form online or calling (256) 474-7550 today.