Leaks & sources

AC condensate line leak: why your air conditioner is dripping inside

Updated September 29, 2026

Short answer

An air conditioner leaks inside when its condensate drain line clogs or its drain pan cracks, so water overflows into the attic, closet or ceiling. Turn the system off, clear the line, and have the ceiling checked for wet insulation.

Attic air handler with an overflowing condensate pan

How it happens

The indoor coil pulls moisture out of the air, and that water drains through a small pipe to the outside or a drain. Algae, dust and scale clog it. Arizona systems run for months, and humid monsoon weeks produce even more condensate.

What to do now

Turn the AC off at the thermostat.
Put towels or a bucket under drips.
Check the outside end of the condensate line: if it isn't dripping while the AC runs, the line is probably clogged.
Look at the secondary pan (if accessible) for standing water.

Clearing the line

Use a wet-dry vac on the outside end of the line to pull the clog out.
Pour a cup of white vinegar into the access port near the air handler.
If it clogs repeatedly, have an HVAC technician check the slope and the trap.

Protecting the ceiling

Attic air handlers should have a secondary drain pan and a float switch that shuts the AC off when water rises. Ask an HVAC technician to confirm both are installed and working during a tune-up.

Questions

Can I run the AC while it's leaking?

Better not — it adds more water. In extreme heat, get the line cleared quickly.

How often should I clear the condensate line?

Many homeowners flush it with vinegar a few times a year, especially before summer.

Is wet attic insulation a problem?

Soaked blown-in insulation usually needs replacement and can lead to mold if left.

Editorial note: this guide is general information for Arizona homeowners, not professional, legal or insurance advice. For your situation, talk to a licensed contractor and your insurer.