How to Unclog Your AC Condensate Drain Line
Your air conditioner pulls a surprising amount of moisture out of the air — gallons on a humid day. All that water drains out through a small PVC line, usually running from your indoor unit to somewhere outside. When that line clogs with algae and gunk, the water has nowhere to go, and it ends up on your floor, in your ceiling, or tripping a safety switch that shuts the whole system down.
Symptoms of a clogged drain
- Water pooling around the indoor unit or in the drain pan
- The AC shuts off unexpectedly (a float switch detected rising water and killed the system to protect you)
- Musty smells near the air handler
- Water stains on ceilings or walls below the unit
If your AC suddenly stopped and you can't figure out why, check the drain before you call anyone. It's the cause more often than people expect.
How to clear it
- Turn off the AC at the thermostat (or the breaker if you want to be thorough). You're working around water and electricity — don't combine them.
- Find where the drain line ends. It's usually a small PVC pipe dripping near the outdoor unit or along the foundation. If it's dripping steadily while the AC runs, it's flowing. If it's dry while the AC runs, it's probably clogged. Note: some systems don't drain outside at all — the line may tie into a bathroom sink drain or another plumbing fixture. If you can't find an outside end, check under nearby sinks.
- Hook up a wet/dry vacuum to the outside end of the line. Wrap a rag around the connection to get a decent seal, and let it suck for two to three minutes. You'll often hear the clog break loose. (If your line ties into a sink drain instead of running outside, skip this step and clear it from the inside access tee in the next step.)
- Flush the line from the inside. Back at the indoor unit, find the drain line's access tee (a short vertical PVC stub with a cap, near the air handler). Pour in a cup of distilled white vinegar. Let it sit for about 30 minutes, then flush with water.
- Repeat monthly during cooling season. A cup of vinegar once a month takes two minutes and prevents most clogs from ever forming.
Call a pro when…
- The line is cracked, broken, or disconnected
- Water has gotten into walls or ceilings (that's a damage question, not just a clog)
- The float switch keeps tripping even after you've cleared the line
- You can't find the drain line or the access point
This is a ten-minute job that prevents thousand-dollar water damage. I show the whole process on video at HVAC DIY Help on TikTok and YouTube (@hvac_diy_help).