Why Is My AC Leaking Water?

Where the water comes from

Cooling air also removes humidity. As warm, humid air crosses the cold evaporator coil, moisture condenses on it much like water on a cold glass. That water drips into a drain pan and runs out through a condensate drain line, usually a PVC pipe that exits outside or ties into a plumbing drain. In humid weather, a system can remove several gallons of water a day, so a small blockage can become a leak quickly.

Common causes of a leaking AC

Clogged condensate drain line

Algae, slime, dirt and debris can build up and block the line. When that happens, water backs up, fills the pan and overflows. This is the leading cause of indoor AC leaks, particularly in humid climates like ours.

Frozen evaporator coil

If the coil freezes because of poor airflow or low refrigerant, it builds up ice. When the system shuts off or the ice melts, more water arrives than the pan can handle. A leak that comes with weak airflow or visible ice usually points to this cause.

Damaged or rusted drain pan

Older drain pans, especially metal ones, can rust through or crack, and water leaks directly from the pan. This is common in older systems.

Disconnected, cracked or poorly sloped drain line

A drain line that has come loose, been damaged, or does not slope properly can leak or fail to drain. Installation shortcuts show up here.

Dirty filter and airflow problems

A clogged filter can cause the coil to ice, leading to leaks as described above. Dirty coils and blower problems can have the same effect.

Attic and closet installations

In many Houston-area homes the air handler is in the attic or a closet. A leak there may not be noticed until water stains a ceiling, and a hot, humid attic can accelerate algae growth in the drain. A secondary pan and a float switch are important for these installations.

What you can safely check yourself

1. 1Turn the AC off at the thermostat to stop producing condensate. If water is actively dripping from a ceiling, turn the system off and place a bucket underneath. Do not touch electrical components near the water.
2. 2Check and replace a dirty air filter.
3. 3Look for ice on the indoor unit or the refrigerant line. If you see ice, leave the system off and set the fan to On to help it thaw.
4. 4Check whether the secondary drain pan under the unit has water in it, which is a sign the primary drain is blocked.
5. 5If your system has an accessible condensate cleanout, a technician can show you how to clear it with a wet-dry vacuum at the drain line's outside end. If you try a cleaner, a cup of distilled white vinegar is commonly used. Never mix vinegar with bleach, and follow your manufacturer's guidance on chemicals.
6. 6Check whether a float switch has shut the system down. A tripped float switch usually means the drain is blocked and is doing its job.

What a technician actually does

A technician will usually clear the drain line with a vacuum or pressurized flush, inspect the pan and slope, check the float or overflow switch, and look at the coil and filter. If the leak came from a frozen coil, they will find out why it froze, whether from airflow or refrigerant, because clearing the drain does not fix the underlying cause. They may also recommend a cleanout access point, an insulated drain line, or a float switch if your system does not have them.

Preventing leaks in a humid climate

• Change filters on schedule.
• Have the drain line inspected and cleared during seasonal maintenance.
• Make sure your system has a working float switch or overflow safety so it shuts off before water damages your home.
• Insulate drain lines in attics where condensation on the outside of the pipe can drip.
• Do not ignore small stains or a musty smell near the unit, which can signal a slow leak.

In a climate where AC runs for most of the year, a drain line rarely stays clean forever. A small, regular maintenance step costs far less than ceiling and drywall repair.