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Quick answer
An air conditioner pulls water out of the air, and an indoor leak usually means that water is not draining: a clogged condensate line, a full or damaged drain pan, or a frozen coil leaving puddles as it thaws. Turn the AC off at the thermostat or breaker and soak up the water. [2] Change a dirty filter, then clear the drain line or call an HVAC technician. If the unit sits in an attic, check the ceiling below, because an overflowing pan can damage ceilings and drywall. [2]
Do this first: turn it off and catch the water
Every running AC makes water. InterNACHI, a home inspector association, says an evaporator coil can produce up to 50 gallons of water on a very hot, humid day. [1] When that water stops draining, it keeps coming as long as the system runs.
Switch the system from COOL to OFF at the thermostat. Trane says to turn the air conditioner off at the thermostat or circuit breaker box as soon as you notice a drain problem. [2]
Check for electricity near the water. If water is near outlets, cords or the panel, do not enter the water. Turn power off at the panel only if you can reach it from a dry spot; otherwise call the utility or an electrician. CDC says not to enter standing water to reach the main power switch; call an electrician instead. [3]
Soak up water in and around the drain pan with rags or a wet/dry vacuum, the same way Carrier describes its technicians emptying a full pan. [4]
If the air handler is in the attic, check the ceiling below it. Put a bucket under any drip and keep people out from under a ceiling that sags.
Look at the coil and the copper lines. If you see ice, leave the cooling off and read the frozen coil section below.
Take photos of the water, the unit and any ceiling or floor damage before you clean up. [5]
Water coming through a ceiling or a light
Water from an attic unit can soak through drywall and reach light fixtures. Do not touch a wet fixture or switch, and stay out from under a sagging ceiling. If water is near outlets, cords or the panel, do not enter the water. Turn power off at the panel only if you can reach it from a dry spot; otherwise call the utility or an electrician. The guide to water coming through a ceiling light fixture covers this case step by step.
Why is my AC leaking water inside?
Trane explains the path: as the system cools, condensation forms at the indoor unit, drips into the drain pan, then flows out through the condensate drain line, a PVC pipe that drains outside. That line may run through a crawl space or attic, or under a basement floor. [2] A leak means something on that path failed.
Common causes of an indoor AC leak, what you notice, and the next step
Cause
What you notice
Next step
Clogged condensate drain line
Puddles near the indoor unit, a musty smell when the AC runs, poor cooling
Turn the AC off, then clear the line or call a technician
Drain pan full and safety switch tripped
The AC shut off and the pan holds water
Clear the clog so the switch can reset
Frozen evaporator coil
Ice on the coil or lines, warm air, puddles as it thaws
Cooling off, do not chip the ice, call for repair
Dirty air filter
Weak airflow; can lead to a frozen coil
Replace the filter
Water from an emergency drain pipe outside, near a doorway or walkway
The backup drain on an attic unit is carrying water
The main drain has a problem; have it cleared
Condensate pump not working (if you have one)
Water around the small pump box near the unit
Make sure it is clear of debris and running
Rust on the bottom of the indoor unit
Water damage near the unit, a symptom Trane lists for a clogged drain
Have a technician inspect the pan and drain
Table sources: Trane [2][6], Carrier [4] and the U.S. Department of Energy. [7]
Clogged drain line or full drain pan
Trane says the drain line can clog with mold and mildew that form in standing water in the drain pan, or with dust, dirt, dander and debris. [2] Carrier describes the same buildup as a sludge of dust mixed with the moisture the AC removes. [4]
Why the AC may have shut itself off. Trane says some homes have a drain pan safety switch that shuts the indoor unit down when water in the pan begins to rise. Without one, the system keeps running with a clogged drain line until the pan spills over, which could damage ceilings or drywall depending on where the unit is. [2] Carrier calls it a safety float switch and says modern systems often have one. [4] The Department of Energy notes a clogged drain can cause the equipment to turn off until the drain has been cleared. [8] So an AC that quit with a pan full of water usually points to a drain clog.
Attic units. Carrier quotes an HVAC contractor who says attic systems are often piped to an emergency drain that exits outside near a sidewalk, doorway or another visible spot, and water coming from it is usually a sign of a problem. [4]
Carrier recommends calling a technician when you see signs of a clog, but it also gives these steps for a simple one [4]:
Turn the AC off.
Find the drain line access point near the indoor unit and the drain line exit outdoors.
Use a wet/dry vacuum at the outdoor exit to pull the clog out, or pour a cup of distilled vinegar into the indoor access point to dissolve buildup. Hot, not boiling, water can also loosen minor buildup.
If the clog does not clear, or the pan fills again, Carrier says a professional HVAC technician is needed to clear deep blockages.
For prevention, the Department of Energy suggests periodically flushing the drain line with bleach and water to prevent mold growth [7], while Trane and Carrier suggest asking your technician to show you how to pour a cup of distilled vinegar down the line. [2][4] Pick one, never both. CDC says never to mix bleach with ammonia or any other cleanser. [9] Trane also says DIY repair could void your warranty, so check yours first. [2]
Frozen coil: the leak that shows up as the ice melts
Trane lists the signs of a frozen evaporator coil: the AC runs but blows warm air, the coil or its cabinet is iced over, or the refrigerant lines at the outdoor unit are frozen. You may also see puddles on the floor as the coil thaws. [6]
Switch the thermostat from COOL to OFF. Trane says running the system with a frozen coil can cause major damage. [6]
Do not chip away at the ice. It can damage the coil. [6]
Put towels, a tub or a pan under the unit to catch the melt water.
Replace a dirty filter and keep your air vents clear; Trane lists a dirty filter and blocked return vents among the causes of restricted airflow. [6]
Trane says the biggest reason a coil freezes is restricted airflow, and lists a clogged or dirty filter, blocked return vents, a dirty coil, low refrigerant and thermostat issues as causes. Low refrigerant only happens if there is a leak or the unit was charged wrong at installation. [6] The Department of Energy says a trained technician should fix refrigerant leaks, test the repair and charge the system correctly. [7]
What you can safely do, and what to leave to a technician
You: change the filter. If you are unsure how often, the Department of Energy says every month or two during the cooling season, more often with pets or dust. [8] ENERGY STAR says to inspect, clean or change filters once a month. [10]
You: keep supply and return vents clear, soak up water around the unit, and clear a simple clog from the outdoor end with a wet/dry vacuum. [4]
You: if your system has a condensate pump, make sure it is clear of debris and operating properly. [7]
Technician: anything involving refrigerant, a coil that freezes again after a new filter, cleaning the indoor coil, a cracked or rusted pan, and wet wiring. DOE says regular maintenance from a qualified HVAC contractor should include inspecting the coil and cleaning it as necessary. [8]
Technician: a drain that clogs again soon after you clear it. ENERGY STAR says a maintenance check-up should include checking the condensate drain, since a plugged drain can cause water damage in the house and affect indoor humidity levels. [10]
Safe to do yourself
A small puddle by a closet or basement unit, a dirty filter, and a drain that runs freely again after a wet/dry vacuum at the outdoor end is a homeowner fix. Dry the floor, watch the pan for a day, and keep the drain line flowing.
Dry out the water damage
EPA says that if wet or damp materials are dried within 24 to 48 hours after a leak, in most cases mold will not grow. [11] EPA also says to keep AC drip pans clean and drain lines unobstructed, and its duct cleaning guide adds that substantial standing water or debris in the condensate pan indicates a problem requiring immediate attention. [11][12]
Ceiling under an attic unit: EPA's water damage table says wet fiberglass or cellulose insulation should be discarded and replaced, and wallboard may be dried in place only if there is no obvious swelling and the seams are intact. [13] NC State Extension says drywall should be dried within 48 hours. [14]
Drywall that stays wet: the Massachusetts quick reference says to cut out and discard wallboard that has not been sufficiently dried within 48 hours. [15]
Insulation near the coil or in the ducts: EPA says to check insulation near cooling coils for wet spots, and that wet or moldy duct insulation cannot be effectively cleaned and should be removed and replaced. [12]
A musty smell afterward: Carrier lists musty odors from the unit or vents as a sign of a clogged drain. [4] If it lingers after drying, see the guide to mold in air vents.
Insurance. The Insurance Information Institute lists accidental discharge of water from an air conditioning system among the perils covered by common policy types such as the HO-3. [16] The Texas Department of Insurance says policies usually do not cover gradual leaks or seepage [5], and lists wear and tear or maintenance among common exclusions. [17] Check your own policy and report damage promptly.
Common questions
Is it bad if my AC is leaking water inside?
It is a problem to fix quickly. The water is condensation that should be draining outside, and Trane says an overflowing pan can damage ceilings or drywall depending on where the unit sits. [2] Turn the AC off and find the cause.
Can I run my AC if it is leaking water?
Turn it off until you find the cause. Trane says to turn it off at the thermostat or breaker as soon as you notice a drain problem, and that running it with a frozen coil can cause major damage. [2][6]
How do I unclog my AC drain line?
Carrier says to turn the AC off, then use a wet/dry vacuum at the outdoor end of the line, or pour a cup of distilled vinegar into the indoor access point. If that fails, call a technician. [4]
Why did my AC stop working when the drain pan filled with water?
Carrier says modern systems often have a safety float switch that shuts the system down when a clog fills the drain pan, to prevent water damage to ceilings or floors. [4] Clearing the clog lets the water drain so the system can run again.
How often should I change my AC filter?
Follow the maker's guidance. If unsure, DOE says every month or two during the cooling season [8], and Trane says every one to three months depending on the filter. [6]
Does homeowners insurance cover water damage from an AC leak?
The Insurance Information Institute lists accidental discharge or overflow of water from an air conditioning system as a covered peril on common policy types such as the HO-3, and says policies will not cover damage due to lack of maintenance. [16] The Texas Department of Insurance says damage from gradual leaks or seepage usually is not covered. [5] Check your own policy.
Sources
Heating and A/C OverflowInterNACHI (International Association of Certified Home Inspectors), accessed October 12, 2026
