Symptom guide
Water leaking from the AC: where it comes from and what to do today
By the HeatAndAirCost editors · Last updated October 5, 2026 · How we research prices
What people commonly report
A puddle beside the indoor unit in a closet or basement. A water stain spreading on the ceiling under an attic unit. A filter that comes out soaked. Trane points out that an air handler tucked away in an attic or utility room can drip for a while before anyone notices[1]. Some condensation is part of cooling. Water on the floor is not, by Trane’s account[1].
What to do in the first hour
- Turn the system off at the thermostat or the circuit breaker. Trane says this stops more water from leaking and keeps the system from being damaged by running[1].
- Get the water up. Trane suggests a wet/dry shop vac for a lot of water and an old towel for a small puddle[1].
- Start drying. EPA says to dry water-damaged areas and items within 24 to 48 hours to prevent mold growth[5].
- Look at the filter. If it is wet and the unit is dripping onto it, Trane says a frozen coil is the cause[1].
What manufacturers and federal sources say the causes can include
- Cracked or clogged condensate drain pan. The pan under the coil catches condensation and feeds the drain line. A clogged, cracked or rusted pan can leak or overflow[1].
- Clogged condensate drain line. Dirt, debris or growth blocks the line that carries water outside, and the pan overflows[1]. ENERGY STAR’s tune-up checklist includes inspecting the condensate drain because “a plugged drain can cause water damage in the house and affect indoor humidity levels”[3].
- Frozen evaporator coil. A dirty filter, dirty coil, low refrigerant or a refrigerant leak can freeze the coil, and the melt drips[1]. Trane lists puddles near the indoor drain pan among the signs of frozen coils[6].
- Low refrigerant or a leak. Trane ties low charge to frosting and dripping, and says a newly installed unit that leaks may have been installed so condensate does not reach the pan properly[1]. Refrigerant work requires an EPA Section 608 certified technician[7].
How to find out which one it is
You can see some of this without tools. Wet filter or visible frost points to the coil. Standing water in the pan points to the drain. If the system shut itself off and will not restart, it may have a condensate overflow switch: Trane explains that the switch shuts down the outdoor compressor, the condenser fan and the indoor fan when water backs up[2], which is covered on our AC not turning on page.
For routine upkeep, DOE’s cooling guidance is to “occasionally pass a stiff wire through your unit’s drain channels to prevent clogs”[4]. A cracked pan, a refrigerant problem, or a coil that freezes again after thawing is a technician job.
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Try this while you wait
Trane names a wet/dry vacuum for cleanup. A battery water-leak alarm set on the floor by the unit is a way to hear about the next drip early. Neither one fixes the drain or the coil.
As an Amazon Associate we earn from qualifying purchases. It does not change your price. These are screening or upkeep items. None of them is a repair, and none replaces a licensed technician.
When to stop and call
- Water is reaching a ceiling, wall or flooring.
- The drain pan is cracked or rusted through.
- The coil is frozen, or freezes again after it thaws.
- The system keeps shutting off on its overflow switch.
Related guides
What the repair can cost
Related problems
Sources
- Trane: Air handler dripping water
- Trane: HVAC air handler overflow switch
- ENERGY STAR (EPA/DOE): Heating and cooling maintenance checklist
- U.S. Department of Energy: Energy Saver 101, home cooling (PDF)
- U.S. EPA: A brief guide to mold, moisture and your home
- Trane: Top causes of frozen AC coils
- U.S. EPA: Section 608 technician certification requirements
This page is general information collected from the official and manufacturer sources listed above. It is not an inspection or a diagnosis of your system, and only a qualified technician who sees the equipment can tell you what is wrong. HeatAndAirCost is not affiliated with the EPA, the U.S. Department of Energy, ENERGY STAR, Trane. Found an error? hello@heatandaircost.com.
Getting local help
Finding a qualified technician
We do not inspect systems, rate contractors, or recommend any particular company. Whoever you call, ask for the license number and look it up on your state or county licensing board’s public site before work starts. Refrigerant work also requires an EPA Section 608 certified technician. Our contractor hiring checklist covers licenses, insurance, written quotes and red flags.
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People also ask
AC leaking water: FAQs
Why is water leaking from my AC inside the house?
Trane names four sources for an air handler that drips: a cracked or clogged condensate drain pan, a clogged condensate drain line, low refrigerant or a refrigerant leak, and a frozen evaporator coil. A wet filter under a dripping unit points to a frozen coil.
Should I turn off my AC if it is leaking water?
Trane's first step is to turn the system off at the thermostat or the breaker, so no more water leaks and the system is not damaged by running. Then clear up the water with a wet/dry vacuum or towels and call for service.
How fast does AC water damage turn into mold?
EPA says to dry water-damaged areas and items within 24 to 48 hours to prevent mold growth, and that in most cases mold will not grow if wet materials are dried within that window.
What is an AC float switch or overflow switch?
Trane describes it as a safety switch in or on the condensate drain pan. When water backs up, it shuts down the outdoor compressor, the condenser fan and the indoor fan. Not every system has one, and Trane suggests having a technician add one after an overflow.