AC leaking water? Stop the damage, then find the cause

Right now

1. Turn the system off at the thermostat. If water is near electrical parts, turn it off at the breaker as well.
2. Put towels down and a bucket under the drip, and move anything valuable out of the way.
3. Look at the pan under the air handler. If it's full, the drain line is almost certainly clogged.
4. Take photos before you clean up, in case you make an insurance claim.

Mold can start on wet drywall and carpet within 24–48 hours (EPA mold guide), so dry things out quickly with fans.

The causes

Clogged condensate drain (the usual one)

Algae and sludge grow in the drain line in our humidity. The water backs up, fills the pan, and either trips the float switch (the AC suddenly stops) or overflows. Many lines have a cleanout cap near the air handler. A cup of white vinegar there every couple of months helps prevent it, but a line that's already fully clogged usually needs to be cleared with suction from the outside end.

Rusted or cracked drain pan

Older metal pans rust through; plastic ones crack. You'll see a slow, steady drip even though the line is clear.

A frozen coil melting

If the coil froze, a lot of water arrives at once when it thaws. Fix the reason it froze (see frozen AC coil) as well as the water.

Disconnected drain or missing trap

Common after attic or roof work, or on a new install done in a hurry. The water goes into the ceiling instead of outside.

Sweating ducts or air handler

Uninsulated or poorly sealed ducts and cabinets in a humid attic or closet collect condensation on the outside and drip.

The safety switch that should have caught it

A float switch (or secondary pan with a switch) shuts cooling off when water backs up, before it overflows. If your system leaked without shutting itself off, the switch is missing, stuck or wired wrong. We test it on every visit and at every install.