How do you keep an AC condensate line clear?
Updated August 2026
You keep a condensate line clear by flushing it at least twice a year with vinegar or a wet/dry vac, and by checking the drain pan and float switch each cooling season. The line carries the water your AC and high-efficiency furnace pull out of the air, and algae loves that damp PVC, so it slimes shut if you ignore it. A clog that backs up is a $300–2,000 repair once it trips the system off or drips through a ceiling. Ten minutes twice a year prevents it.
| Task | Interval | Effort |
|---|---|---|
| Pour a cup of vinegar down the access tee | Every 1–3 months in season | 5 min · DIY |
| Suck the line clear with a wet/dry vac at the outlet | Twice a year | 10 min · DIY |
| Task | Interval | Effort |
|---|---|---|
| Confirm the drain pan is dry and rust-free | Seasonally | 2 min · DIY |
| Test the float switch shuts the system off | Yearly | 5 min · DIY |
| Task | Interval | Effort |
|---|---|---|
| Clear a stubborn clog with the vac or a CO2 blaster | When backed up | 15 min · DIY |
| Drop algae tablets in the drain pan | Every 1–3 months | $10–15/year |
What neglect costs
Algae and slime narrow the line until water has nowhere to go. Best case, a float switch senses the backup and shuts the AC off, leaving you with no cooling until you clear it. Worst case, there is no switch, the drain pan overflows, and water runs into the ceiling below: the resulting drywall, insulation, and mold repair runs $300–2,000, more if it hits a finished room. The fix is a $5 jug of vinegar and ten minutes, which is why this is the highest-leverage HVAC habit there is.
Leave these to a pro
This is nearly all DIY, which is the point: a wet/dry vac at the outdoor termination and a cup of vinegar at the indoor access tee handle routine clearing. Call a pro ($75–150) only when the line is fully blocked and a vac will not pull it, when the drain pan is rusted through, or when the float switch has failed and needs replacing. If you keep tripping clogs, a tech can add a cleanout tee or reroute a poorly sloped line so it drains on its own.
This whole checklist ships as reminders in OnOtto: every task above, on the right schedule for your home, snooze-proof.
Load this checklist as remindersFrequently asked questions
How do I unclog an AC condensate drain line?
Find the outdoor end where the PVC exits near the condenser, hold a wet/dry vac hose over it (a rag makes a tighter seal), and run it for a minute to suck the clog out. Then pour a cup of distilled vinegar down the indoor access tee to kill remaining algae. If the vac will not pull it and the pan is overflowing, shut the system off to stop the flooding and call for service.
What is the float switch on a condensate line?
It is a small safety float, on the drain pan or in the line, that senses rising water when the drain clogs and shuts the AC off before the pan can overflow. If your system suddenly stops cooling on a humid day and the pan is full, a working float switch is doing its job, telling you the line is blocked. Not every system has one; adding a float switch is a cheap insurance upgrade against a ceiling leak.
How often should I flush the condensate line?
Pour a cup of vinegar down the line every 1 to 3 months during cooling season, and do a full wet/dry vac clearing at least twice a year, more in hot, humid climates where algae grows fastest. Homes with high indoor humidity or a lot of runtime clog sooner. Algae tablets in the drain pan, about $10 to $15 a year, slow regrowth between flushes. The flush-interval guide covers climate adjustments.