Why is my AC leaking water inside?

By Dana Whitlock. Updated October 2026. Repair or replace?

Air conditioners pull a surprising amount of water out of the air. It collects in a pan under the indoor coil and leaves through a drain line, sometimes with help from a small pump. When any part of that path clogs or fails, water ends up on the floor or the ceiling. DOE warns that clogged drain channels stop the unit from removing humidity and can stain walls or carpet.

Likely causes

A clogged condensate drain line Safe to check

Algae and dust build up in the line over a season. ENERGY STAR's checklist has the contractor inspect the drain each year because a plugged drain can cause water damage and affect humidity. You can look at the visible end of the line where it exits.

A full or cracked drain pan Pro job

An overflowing pan means the line downstream is blocked. A rusted or cracked pan leaks even with a clear line. Pans sit inside the air handler, so replacing one is technician work.

A failed condensate pump Safe to check

In attics and basements, a small pump may lift water to a drain. If it is unplugged or its float sticks, it overflows. Checking power to it is easy.

A frozen coil melting Safe to check

When an iced-up coil thaws, it can dump more water than the pan handles. If you also see ice on the lines, read our page on AC freezing.

A tripped float safety switch Safe to check

Many systems have a switch that shuts cooling off when the pan fills. An AC that stopped cold, with water nearby, may simply mean that switch did its job.

Safe things to check first

• Turn cooling off at the thermostat and soak up the water.
• Find where the condensate line ends (outside near the foundation, or at a floor drain) and look for a visible clog or a dry outlet during cooling.
• Make sure a condensate pump, if you have one, is plugged in and its tube is not kinked.
• Lennox's homeowner guide suggests checking the drain line for clogs monthly, including any auxiliary drain.
• Look for ice on the refrigerant lines. If present, let it thaw before restarting.

When to stop and call

Call a licensed HVAC technician if water keeps coming after the visible line is clear, if the pan is rusted, or if water is near electrical parts or dripping through a ceiling. An attic leak can ruin drywall fast, so do not wait on that one. Avoid opening the air handler, and keep power off at the thermostat until the water is controlled.

Repair or replace?

Start with its age. Type the serial from the label:

Drain clearing and pump replacement are cheap and do not depend on age. A rusted pan inside an old air handler can signal a coil near the end of its life. DOE's analysis puts central AC life at about 24 years in northern and hot-dry climates and 18 in hot-humid ones. Date the system with the age decoder above. A young system gets the repair. An old one with a corroded pan and coil is worth pricing against the replacement range above.