Walk over to your indoor air handler. Is there a thick layer of ice on the copper lines? On the coil itself? Maybe water dripping from the unit onto the floor as it slowly thaws?
That's a frozen AC. And in Florida, where outdoor temperatures sit at 92° most of the summer, it feels deeply weird that an air conditioning system could ice over. But it happens all the time, and the cause is almost always one of four things.
What "frozen" actually means
Your AC works by evaporating cold refrigerant inside the indoor coil (the evaporator). As warm, humid Florida air passes over the cold coil, two things happen: heat transfers out of the air (cooling it), and water vapor condenses on the coil and drips down the drain line.
The coil is normally about 40°F when running, cold, but well above freezing. When something in the system goes wrong, the coil temperature can drop below 32°F, and the water condensing on the coil freezes solid instead of dripping away. Once that happens, no air can pass through the iced-over coil, no cooling happens, and the ice gets thicker as more water condenses on it.
Here's the worst part: a frozen coil can cause the compressor to fail. If the system keeps running with a frozen coil, liquid refrigerant can return to the compressor (which is designed to compress only vapor). That's called slugging, and it's one of the top compressor killers we see. So if you see ice, turn the AC OFF immediately while you figure out the cause.
Set the thermostat to OFF (cool mode off). Turn the fan to ON to circulate warm air across the coil and speed up thawing. Let it run for 2-4 hours. You'll see water in the drain pan as it thaws, that's normal. Don't run cool mode again until all the ice is gone.
Cause 1: Restricted airflow (~60% of cases)
Restricted airflow is the #1 cause of frozen ACs in Florida, and it's almost always one of three things:
- A clogged air filter. When the filter is so loaded with dust that air can barely move through it, the coil gets too cold (because not enough warm air is removing heat from it). Florida AC filters need replacement every 30-60 days for 1-inch filters; 6-12 months for 4-5 inch media filters.
- Closed or blocked vents. Closing vents in unused rooms feels like it should save energy. It doesn't, it actually creates pressure imbalances that can starve the system of return air, leading to the same freeze-up dynamic. Keep vents open.
- A failing blower motor. If the indoor blower can't move enough air across the coil, the same dynamic kicks in. Symptoms: weaker airflow at the vents than you remember, even with a clean filter.
Self-check: after thawing, replace the filter, open all vents, and run the system. If it doesn't freeze up again within 24 hours, you found it.
Cause 2: Low refrigerant (~30% of cases)
When refrigerant charge is low, the pressure in the evaporator coil drops, which makes the coil even colder than normal, low enough to freeze condensation instead of just chilling it. So a refrigerant leak shows up as a freeze-up before it shows up as poor cooling.
The catch: refrigerant doesn't "use up" or evaporate. It's a closed loop. If you're low, you have a leak. Common leak points include the indoor coil itself (especially older units with copper coils), refrigerant line connections, and the outdoor coil. Refrigerant work requires EPA certification and proper recovery equipment. This isn't DIY.
How to know it's refrigerant: if you've replaced the filter, opened the vents, cleaned the outdoor unit, and it still freezes up after thawing, you almost certainly have a leak. Call a tech, they'll do a pressure test and locate the leak with electronic detection.
Cause 3: Dirty evaporator coil (~7% of cases)
The evaporator coil is supposed to stay clean (the air filter is upstream of it for exactly that reason). But over years of use, especially with cheap fiberglass filters or pets, dust and biofilm can build up on the coil itself. That coating insulates the coil from the air passing over it, and you get the same freeze-up dynamic.
Coil cleaning is a tech job, the coil is delicate (the aluminum fins bend easily) and requires specific cleaning products. We do this routinely as part of tune-ups, but it's also a common standalone fix when freeze-ups recur after airflow and refrigerant are ruled out.
Cause 4: Outdoor temperature too low
This one's rare in Florida but worth mentioning. ACs aren't designed to run when the outdoor temperature drops below ~60°F. If you try to run yours during a winter cold snap (we get a few mornings each January in the 40s), the system can freeze up because the refrigerant cycle wasn't designed for that condition.
The fix is simple: don't run the AC when it's cold outside. If you need heat, use the heat-pump or strip-heat side of your system. If you don't have heat, that cold morning is a great time to read about heat-pump options.
How to prevent freeze-ups going forward
Three habits that prevent 95% of Florida freeze-ups:
- Replace your filter monthly during peak cooling season (April-October). Set a phone reminder. Don't trust yourself to "remember."
- Get a twice-yearly tune-up. A tune-up catches refrigerant slow-leaks and dirty coils before they freeze the system. Most freeze-ups would have been prevented by the previous spring tune-up. Our Champions Club includes two tune-ups per year.
- Keep the outdoor unit clear. No bushes within 2 feet, no grass clippings on the coil, no lawn furniture leaning against it. The condenser needs airflow to work properly, even though it's the indoor coil that freezes.
If your AC is currently frozen and you've thawed it but it's freezing again, that's our cue. Call (561) 503-3003 or request a visit online. Same-day service across Palm Beach, Martin, and Broward Counties. Honest diagnosis, written flat-rate quotes, 90-day warranty.
