It's 92 degrees outside, the AC has been running all afternoon, and the house is getting warmer instead of cooler. Then you find frost or a coat of ice on the copper refrigerant line, or even on the indoor coil. It seems backwards, but a frozen AC is a common summer call around Kissimmee and Central Florida, and humidity plays a big part.
How an AC can freeze in hot weather
Your air conditioner cools by sending cold refrigerant through the evaporator coil inside your air handler. Warm indoor air blows across that coil, the air gives up its heat, and the moisture in the air condenses on the coil and drips into the drain pan. That's how your AC dehumidifies your home.
The coil is supposed to stay cold, but above freezing. When something throws the system out of balance, the coil can drop below 32°F. The water condensing on it turns to frost, the frost blocks airflow, the coil gets even colder, and the ice keeps building on itself. In Florida, where the air holds so much moisture for so much of the year, there's plenty of water on that coil to freeze, so once the process starts, ice can build quickly.
The most common causes
Almost every freeze-up comes down to one of two things: not enough warm air moving across the coil, or not enough refrigerant in the system.
- A dirty air filter. This is the first thing to check. A clogged filter starves the coil of warm air, so it gets too cold. Because the AC runs most of the year here, filters fill up faster than many people expect. See how often to change your filter.
- Closed or blocked vents. Closing vents in unused rooms, or covering return grilles with furniture or curtains, cuts down the air moving across the coil.
- A dirty evaporator coil. Dust that gets past the filter coats the coil over time.
- Blower problems. A failing blower motor, a weak capacitor or a dirty blower wheel moves less air. Sometimes the indoor fan isn't running at all.
- Duct problems. A crushed, kinked or disconnected duct in a hot attic can choke off airflow to the system.
- Low refrigerant. An air conditioner doesn't use up refrigerant the way a car burns gas. If it's low, there's a leak. Low refrigerant drops the pressure and temperature in the coil, and ice is a classic sign. Adding refrigerant without finding the leak is only a temporary fix, and finding leaks and handling refrigerant are jobs for a licensed, EPA-certified technician.
- Running the AC on a cool night. On one of our cooler winter nights, running the AC with the thermostat set very low can sometimes let the coil get too cold. If ice only shows up on cool nights, mention it to your technician.
Don't confuse it with heat pump defrost
If you have a heat pump and see a light frost on the outdoor unit on a chilly morning while it's heating, that can be normal. Heat pumps run a defrost cycle to melt that frost. Frost that never clears, or an outdoor unit that's encased in ice, is a different story. That's a job for our heat pump repair team.
What to do if your AC is frozen
- Turn cooling off at the thermostat. A frozen system won't cool the house, and running it this way strains the compressor.
- Set the fan to On. Running just the blower moves room air across the coil and helps it thaw faster. If the blower doesn't run, leave the whole system off and call us.
- Check the air filter. If it's dirty, replace it now.
- Open the vents and clear the returns.
- Get ready for water. As the ice melts, a lot of water heads for the drain pan and drain line. If the drain is partly clogged, it can overflow, so keep towels handy and check around the air handler. Our FAQ explains how to clear a drain line safely.
- Wait for a full thaw. A heavily iced coil can take several hours to thaw completely. Let it clear all the way before switching back to cooling.
Please don't chip, scrape or pry at the ice, and never aim a heat gun or open flame at the coil or lines. The fins and copper tubing are easy to damage, turning a frozen coil into a refrigerant leak.
When to call a pro
If you replaced a dirty filter, the system thawed and it has cooled normally ever since, you may have found the problem. Call us if:
- The ice comes back after thawing, especially with a clean filter
- You hear hissing or bubbling, or see oily residue on the refrigerant lines, which can point to a leak
- The indoor blower doesn't run, or airflow stays weak
- Water keeps overflowing, or the drain safety switch keeps shutting the system off
- A breaker trips
When we come out, we test airflow, refrigerant pressures and temperatures, the blower and the coil, instead of just adding refrigerant and hoping. We explain what we find and give you the price before any work starts. Learn more about our AC repair service.
How to keep it from happening again
Most freeze-ups trace back to airflow or a slow leak, and regular maintenance helps catch both early. Change your filter on schedule, keep vents open, and keep the indoor coil and drain line clean. During an AC tune-up, we check airflow, clean the drain line, look over the coil and check how the refrigerant side is performing. Our Comfort Club maintenance plans include two visits a year, which fits how hard air conditioners work here. If your AC isn't cooling and you don't see ice, start with our list of 7 things to check before you call.
