Why an Air Conditioner Leaks Water

If the air conditioner is cooling, it is making water. The indoor coil runs cold, moisture condenses, and a drain is supposed to carry it to a floor drain, a pump, or a stub-out outside. A leak is that water missing the drain. It is rarely the outdoor unit crying onto the pad, which on a humid morning can just be the cabinet sweating.

The usual indoor causes

• A drain line plugged with algae, especially right after the first hot week.
• A condensate pump that no longer lifts, or a float switch that already shut the system down because the reservoir is full.
• A pan that is rusted through, or a secondary attic pan that is filling because the primary drain failed.
• A coil that froze from low airflow or a low charge, then thawed. The water volume looks dramatic and the drain may be innocent.
• A unit that is not level, so water runs off the back of the pan instead of toward the outlet.

What to do and what to skip

Turn the cooling off so it stops making water. If you can reach a wet-vac on the outside end of a drain that you know is the condensate line, clearing a slimy blockage is sometimes straightforward. Do not cut into a line you cannot identify. Do not pour bleach through the coil. Do not run the system while water is actively hitting a ceiling. A wet switch that has the system locked out is doing its job.

Water plus ice, or water that returns as soon as the drain is cleared, needs AC repair. The drain, the pan, and the reason the coil iced get separated. How much water belongs in the pan is covered in the drip pan note.

Common questions