Quick answer: An AC usually freezes up from restricted airflow (a dirty filter, closed vents or a dirty coil) or low refrigerant, which means a leak. It leaks water when the condensate drain clogs, the drain pan cracks or rusts, or melting ice overwhelms the drain. Check the filter, vents and pan yourself; leave refrigerant and electrical work to a licensed pro.
Why do freezing and leaking often happen together?
Because they’re two stages of the same problem: ice forms on the coil, then melts faster than the drain can handle. Your air conditioner’s indoor coil is supposed to be cold, just not below freezing. As warm, humid air passes over it, moisture condenses into water, drips into a drain pan and flows out through a condensate drain line. On a sticky Central Texas summer day, that can add up to gallons.
If something drops the coil below freezing, that moisture turns to ice instead. When the system shuts off or the ice lets go, far more water comes off the coil than the pan and drain are built for. That’s why a frozen coil and a puddle by the indoor unit so often show up as a pair.
What causes an AC to freeze up?
Usually not enough warm air moving across the coil, or not enough refrigerant in it. The common culprits:
- A dirty air filter. The number one cause. A clogged filter chokes airflow across the coil, so the coil gets too cold.
- Closed or blocked vents and returns. Shutting a bunch of supply vents, or parking the couch in front of a return grille, cuts airflow too.
- A dirty evaporator coil. Dust that sneaks past the filter builds up on the coil and blocks both airflow and heat transfer.
- Blower problems. A failing blower motor, a weak capacitor or a dirty or slipping blower wheel can all reduce airflow.
- Duct problems. Undersized, crushed or disconnected ducts, common in hot Austin attics, can restrict airflow.
- Low refrigerant. Air conditioners don’t use up refrigerant. If the charge is low, there’s a leak somewhere, and the lower pressure can make the coil freeze.
- Running the AC when it’s cool outside. Cooling on a chilly night, especially with the thermostat set very low, can contribute to freezing on some systems.
Why is my AC leaking water?
Most of the time the drain is clogged and the water is backing up. Here’s what to look for:
- A clogged condensate drain line. Algae, slime, dust and debris build up in the line over time, and our long, humid cooling season gives them plenty of time. When the line backs up, the pan overflows.
- Water in the secondary drain pan. Many attic air handlers sit in a secondary pan as a backup. Water in that pan means the primary drain isn’t doing its job.
- A float switch that shut the system off. Many systems have a safety float switch that turns the AC off when water rises in the pan or drain. If your AC quit cooling and there’s standing water nearby, the switch probably did exactly what it’s supposed to.
- A cracked or rusted drain pan. Older metal pans can rust through after years of catching condensate.
- A melting frozen coil. Covered above: the ice can release more water than the drain can take.
- A disconnected or poorly sloped drain line. A line that has come apart, sags or was installed without enough slope can leak or back up.
- Condensation on uninsulated ducts or lines. Sweating ductwork or refrigerant lines in the attic can drip onto the ceiling below.
For more on this topic from our main site, see Why Is My Air Conditioner Leaking Water? and Why Is My AC Freezing Up?
What can homeowners safely check?
Quite a bit, starting with the filter. If you see ice on the indoor coil or refrigerant lines, or water near the indoor unit:
- Turn the cooling off. Set the thermostat to off (or cooling off) so the system stops making more ice. Many technicians suggest switching the fan to “on” to help it melt faster. Even so, thawing can take several hours.
- Protect the area. Put towels or a shallow pan under the unit and move belongings away from the leak. If water is coming through a ceiling, turn off cooling and call for service promptly to limit the damage.
- Check the air filter. If it’s dirty, replace it with the correct size, airflow arrow pointing toward the unit.
- Open vents and clear returns. Make sure supply vents are open and return grilles aren’t blocked.
- Look at the secondary drain pan. If you can safely get to your attic unit, check the pan for standing water. Standing water means the primary drain needs attention.
- Check the outdoor unit. Make sure it runs when cooling is on and isn’t smothered by plants or debris.
Once the ice is completely gone and the filter is clean, try cooling again. If the coil freezes again or the water keeps coming back, it’s time to call a pro.
What should you not try yourself?
Anything involving the coil, refrigerant, safety switches or wiring:
- Don’t chip or scrape ice off the coil. It’s easy to puncture it and turn a frozen coil into a refrigerant leak.
- Don’t add refrigerant or buy a “recharge” kit. The EPA requires technicians who handle refrigerant to be certified, and adding refrigerant without fixing the leak only delays the problem.
- Don’t bypass or disconnect a float switch to get the AC running. It’s there to keep water out of your ceiling.
- Don’t open electrical panels or work on wiring inside the unit.
When should you call an HVAC technician?
When the easy fixes don’t hold, or you see signs of a leak or water damage:
- The coil or refrigerant lines freeze again after you’ve replaced the filter.
- Ice shows up on the outdoor unit’s lines in summer.
- Water keeps collecting in the secondary pan, or the float switch keeps shutting the system off.
- A water stain appears on the ceiling below the attic unit.
- You hear hissing or bubbling, or the system cools poorly even with good airflow, which can signal a refrigerant leak.
- The drain pan is rusted or cracked.
A technician can test airflow and refrigerant pressures, find and repair leaks, clean the coil and drain, check the float switch and inspect the pan. Regular maintenance, including clearing the condensate drain, lowers the odds of all this happening in the middle of July.
The bottom line
A frozen or leaking AC almost always points to an airflow, refrigerant or drainage problem. Start with the safe checks: turn off cooling, let the ice melt, replace the filter, open vents and look for standing water. If the problem comes back, or you see signs of a refrigerant leak or water damage, call a licensed technician before a small problem turns into a big one.
Frequently asked questions
Is it safe to run my AC if it’s frozen?
No. Running a frozen system cools worse and can strain the compressor. Turn cooling off and let the ice melt before running it again.
How long does it take a frozen AC to thaw?
Often a few hours, and longer with heavy ice. Running the fan with cooling off can speed it up.
Why does my AC shut off when water is in the drain pan?
Many systems have a float switch that turns the AC off when water backs up. It’s a safety feature to limit water damage, and the drain has to be cleared before the system will run normally.
Can low refrigerant cause both freezing and leaking?
Yes. Low refrigerant can make the coil freeze, and when the ice melts it can overflow the drain pan. Since low refrigerant means a leak, a technician needs to find and repair it.
Related guides: What’s Included in an HVAC Tune-Up?, How Long Does an AC Last in Central Texas? and Best Practices for Mold Prevention in Your HVAC System.
About Gold Eagle Services: This guide comes from the team at Gold Eagle Services, a family-run Austin HVAC, indoor air quality and mold remediation company founded in 2017. We’re licensed (TACLA119235 and RCO1783), insured and bonded, and we serve homes across the greater Austin area.
Need help with this in your home? Learn about our air conditioning repair and installation, or call 512-489-4653 to schedule a visit.
