Short answer: The drain line carries the water a mini split pulls out of your air to the outdoors. When algae, dust or mold block it, water backs up and drips from the indoor unit. If your filter is clean and water still appears, suspect the drain line. A wet/dry vacuum at the outdoor end is the simple fix makers describe.
What the drain line does
In cooling mode, the indoor coil pulls moisture out of the air. Carrier explains that this water collects in a drain pan and leaves through a drain line. Trane describes the same path: water flows into the pan, then into the condensate drain line or PVC pipe, and drains outside.
Over time, algae, dust and mold can build up in the line. Carrier says that when the water cannot exit, it backs up and overflows the pan. Bryant says dirt and dander from the room are pulled into the drain, and that it sometimes needs cleaning several times a year.
Signs the drain line is clogged
- Water pooling under the indoor unit or running down the wall
- A musty smell near the unit (Carrier links this to stagnant water in the line)
- No water coming out of the drain at the outdoor end during a humid day of cooling
- The filter is clean, but the leak keeps happening
Check the filter first. A dirty filter can freeze the coil, and the melting ice can overflow the pan too, according to Carrier and Trane. See how to clean a mini split.
Safe things to try
Put on old clothes, grab a bucket, a towel and a flashlight, and take your time. Go in this order.
- Turn the mini split off at the remote before you do anything. Put towels or a bucket under the leak.
- Find the outdoor end of the drain line. It is usually a small hose or pipe on the outside wall near the indoor unit. Walk the outside wall below the indoor unit until you spot it.
- Look for kinks, crushing or a loose connection you can see from outside. Trane says to replace a cracked line. A cracked or disconnected line is a repair.
- Use a wet/dry vacuum on the outdoor end of the line. Carrier says to suction out debris from the end of the line. Hold the hose tight against the end for about a minute. You may pull out slime, dirt or insects, and that is a good sign.
- Optionally, pour a warm water and vinegar mix through the line. Carrier lists this as an alternative for breaking up organic buildup. Do not use harsh chemicals unless your manual says so.
- Restart the unit and watch for a few hours. Expected result: you see water dripping or running out of the outdoor end while the unit cools, and the indoor leak stops.
Keeping the line clear
Bryant recommends checking the drain line monthly and cleaning filters every two to four weeks. Keep soil, mulch and leaves away from the outdoor end so it can drain freely.
When to stop and call a technician
- The leak continues after you clear the line
- The drain pan looks cracked, rusted or tilted (Carrier and Trane both say a damaged pan needs a professional)
- The indoor unit is not level, or the line does not slope down. Carrier says that needs installer adjustment
- You see ice on the coil or lines. Trane and Bryant say to turn the unit off and let it thaw. Ice can point to an airflow or refrigerant problem
- The unit shows a drain or water level error. For example, Fujitsu code 53 is a drain pump error and LG code CH04 is a drainage error. See Fujitsu error codes and LG error codes
- Your system uses a condensate pump. See mini split condensate pump
Do not open the cabinet, probe inside the unit, or touch the electrical parts. A pro clears the line from the inside when the outside method does not work.
For the full list of leak causes, read mini split leaking water.
Related reading
- Water sounds are not always a clog, so read about gurgling noises when off.
Sources
Follow your unit's own manual. This is general information.
