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How do you clear a clogged AC condensate drain line?

Updated August 2026

About 30 minutes · Easy DIY

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Seal a wet/dry vac onto the outdoor end of the line and run it two or three minutes: that pulls the clog, and the whole job takes about 30 minutes including the vinegar flush that stops it coming back. A plugged condensate line is the top reason an air conditioner drips water indoors, and most systems carry a float switch that shuts cooling off once the pan backs up. Clear it at the start of cooling season, then keep it open monthly through summer.

What you need

Before you start: The air handler cabinet holds 120 or 240 volt wiring and you are working around standing water, so cut power at the breaker instead of trusting the thermostat switch. Skip the bleach that gets recommended online: it corrodes metal drain pans, attacks the coil, and can soften glue joints in older PVC. Vinegar does the same job without the damage. Do not blow compressed air backward into the line either, since pressure can pop a glued joint inside a wall. If the pan is rusted through, or water is coming from somewhere other than the pan, call a tech.

Steps

  1. Shut the system off at the thermostat and cut power at the air handler switch or breaker. If a float switch already tripped, the system is off and the reason is sitting in the pan.
  2. Find both ends. Indoors, look for the 3/4 inch white PVC pipe leaving the air handler with a capped access tee a foot or two downstream. Outdoors, that pipe ends near the foundation, often within a few feet of the condenser.
  3. Sponge or vacuum the standing water out of the drain pan first so nothing overflows while you work.
  4. Seal the shop vac hose onto the outdoor pipe with a rag or a wrap of duct tape and run it 2 to 3 minutes. Expect a slug of black sludge when the clog releases.
  5. Uncap the indoor access tee and pour in a quart of warm water. If it runs straight out the far end, the line is open.
  6. Pour a cup of distilled white vinegar down the tee, let it sit 30 minutes, then flush with warm water. That kills the algae film that grows the next clog.
  7. Recap the tee, dry the pan, and confirm the float safety switch has dropped back to its reset position.
  8. Restore power, run cooling 15 minutes, and check the outdoor pipe. A working system drips steadily, and 5 to 20 gallons a day of condensate is normal in a hot, humid climate.
  9. Put a cup of vinegar down the access tee once a month for the rest of the season. Two minutes each time.

Or hire it out

Clearing a condensate line as a standalone call runs $75 to $250, higher on an August weekend. Compare that with what an overflow does: a soaked ceiling is $500 to $3,000 once drywall, paint, and insulation are counted, and a saturated attic climbs from there.

Done. Now the part everyone skips: doing it again on schedule. Log it in OnOtto and the next reminder for AC drain line flushes sets itself.

Log this task, get the next reminder

Frequently asked questions

Why did my AC shut itself off when the line clogged?

A float switch did its job. Most systems carry a small float in the primary pan or on the secondary drain, and when water rises it breaks the 24 volt thermostat circuit and stops the call for cooling. Annoying in July, far cheaper than a ceiling. Resetting it without clearing the line just refills the pan within hours. Why a condensate drain line clogs covers what is growing in there.

Bleach or vinegar?

Vinegar. Distilled white vinegar kills algae and biofilm without harming the pan, coil, or pipe joints, and a gallon costs about $4. Bleach corrodes galvanized and aluminum pans, and repeat doses can damage the evaporator. For something longer lasting, condensate pan tablets run $10 to $20 for a season and dissolve slowly in the pan. Use one approach or the other, not both at once.

How often should I flush the drain line?

Once a month during cooling season, plus a full clearing at the start of it. Humid climates that run the AC eight or nine months a year need the monthly habit most, because the line never dries out. How often to clean an AC condensate drain line has the schedule, and the condensate drain line checklist lists what else to inspect while you are down there.

It clogged again a month later. What am I missing?

Usually slope or insulation. The line has to fall continuously toward its outlet, and a sagging horizontal run or a strapped-up loop holds water that grows a new plug in weeks. An uninsulated line in a hot attic sweats and drips, which people mistake for a fresh clog. Check that the outdoor termination is not buried in mulch or blocked by a wasp nest. The cost of ignoring a clogged line shows why this is worth chasing down.

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