You can fix this
Likely cause: a clogged condensate drain line
Dust and moisture build sludge in the drain line until water backs up into the pan. A wet/dry vac and vinegar usually clear it.
Why this happens
As your AC cools, it pulls water from the air and sends it down a small drain line. Carrier says sludge from dust and moisture, along with mold, builds up in that line, and Lennox points to dust and dirt clogs. Once it backs up, the pan overflows or a float switch shuts the AC off.
How to fix it
- Set the thermostat to Off and switch off power to the indoor unit. Lennox, Carrier and Trane all say to turn the AC off first.
- Outside, find where the drain line ends, usually a small PVC pipe near the outdoor unit or foundation. Fit a wet/dry vac hose over the end, seal it with your hand or a rag, and run the vac to pull the clog out.
- Inside, find the access point on the drain line near the indoor unit, often a capped T-shaped fitting. Pour in diluted vinegar, wait at least 30 minutes, then flush it with water, as Lennox describes.
- Wipe out the drain pan and soak up any standing water.
- Stick to vinegar and water. Don't add other cleaners to the line.
- Restore power and run the AC. To keep it clear, Carrier suggests pouring a cup of distilled vinegar into the access point monthly.
When to stop. If the clog won't clear, comes back within weeks, or you can't reach it, Lennox says to call a professional.
If this does not fix it, tell the HVAC technician
- That you vacuumed the line from outside and flushed it with vinegar.
- Whether water still backs up after cleaning.
- Any rust or cracks in the drain pan.
Build the full list: what to tell the HVAC technician.
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