AC leaking water? The 6 causes — and the DIY drain-line fix
An AC leaks water when the condensation it normally drains away gets blocked — most often a clogged condensate drain line — so the water backs up and spills inside instead of running outside. This is drain water, not a refrigerant leak; turn the unit off to stop the damage, then work the causes below.
Standing condensate grows mold within a day or two. Turn the AC off, and if the damage is spreading, call (888) 810-2291 for a licensed local contractor.
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Should you turn the AC off, and is a leak an emergency?
Yes — turn it off to stop the water damage. Treat it as urgent if water is reaching drywall, ceilings, or floors, because standing condensate can start mold within a day or two. Keep in mind this is condensate — the water the AC pulls out of your air — not refrigerant; a true refrigerant leak is an invisible gas, covered on our low refrigerant signs page.
Why does an AC produce water at all?
Cooling pulls humidity out of your air, that moisture condenses on the cold evaporator coil, drips into a pan beneath it, and runs out through a drain line to the outside. A leak means one step in that chain — pan, line, or pump — has failed. Knowing the path is how every cause below fits into place: the water is always trying to reach the outside, and a leak is water that found an easier way down instead.
What causes an AC to leak water?
Six things break that drain chain, ordered here by how often they're the culprit — the first is fixable in twenty minutes, and the rest range from a simple DIY check to technician work.
Clogged condensate drain lineDIY · $0–$250
This is the number-one cause. Dust, mildew, and algae plug the drain line, so the water backs up out of the pan and spills into your home instead of running outside. Look for a PVC stub near the indoor unit and standing water in the pan. You can clear it yourself with a wet/dry vacuum in about twenty minutes (steps below); a professional clearing runs about $75–$250.
Dirty filter or a frozen coil that thawedDIY / PRO · $5–$40+
A dirty filter — or low refrigerant — freezes the evaporator coil, and when that ice melts it overwhelms the drain pan and leaks. This is the classic "it only leaks after I turn it off." Swap the filter (a $5–$40 DIY fix) and check for past icing; if the cause is refrigerant, that's a technician job. The full walkthrough is on our frozen AC coil guide.
Cracked or rusted drain panPRO · $150–$600
The pan under the indoor coil rusts or cracks with age, so it can no longer hold the condensate it collects and the water escapes underneath. Inspect the pan for corrosion or splits. A replacement pan runs about $150–$600 depending on how buried the unit is — technician work on most systems.
Failed condensate pumpPRO · $150–$400
Units in a basement or attic use a small pump to lift the condensate up and out. When the pump fails, the water it can't move spills over the reservoir. Listen for the pump cycling and look for a small box with a float switch. A condensate pump replacement runs about $150–$400.
Disconnected or badly sloped drain lineDIY / PRO · $0–$300
A drain line that slipped loose, lost its downhill slope, or was installed at the wrong angle drains inside instead of outside — common right after a new install. Confirm the line runs continuously downhill to the exterior. A slipped fitting is a DIY reconnect; a re-slope is a modest service call.
Low refrigerant (a leak that freezes the coil)PRO · EPA 608 · $225–$1,600
Low refrigerant lowers the coil temperature until it ices, and the melt then leaks — and a low charge always means a refrigerant leak, never normal use. The tell is weak cooling plus water plus a faint hiss. A find-and-fix with recharge runs about $225–$1,600, and handling refrigerant is EPA Section 608–licensed work. Confirm the symptoms on our low refrigerant signs page.
Cleared the drain and it still leaks?
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How do you clear a clogged AC drain line yourself?
Because a clogged drain line is the most common cause, this is the fix worth trying first — it takes about twenty minutes with a wet/dry vacuum and a cup of vinegar. Work the steps in order:
- Turn the AC off at the thermostat and the breaker before touching anything.
- Find the drain line — a white PVC pipe near the indoor unit, ending outside near the foundation.
- Vacuum the outside end — seal a wet/dry vacuum over the pipe's exit and run it for a minute or two to pull the clog out.
- Flush the line — pour a cup of distilled vinegar into the drain access near the indoor unit to kill the algae that caused the clog.
- Confirm it flows — run water through and check it exits outside, then restart the system.
To make next time easier, a technician can add a T-joint clean-out to the line. One caution: don't repeatedly pour bleach through a metal drain pan — vinegar is gentler and won't corrode it.
Get a licensed AC tech on the phone
One call routes you to a licensed local contractor for an AC water leak — 24/7, nationwide. The call is free.
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When should you call a technician?
Call if the drain-line clear didn't stop it, if you find a cracked pan, a dead condensate pump, or signs of low refrigerant, or if water has already reached drywall or a ceiling. Describe what you already checked — it shortens the visit and the bill, and the diagnostic fee of $75–$200 is often credited toward the repair. What happens on the visit is covered in what to expect from a service call.
What does fixing an AC water leak cost?
A drain-line clear is free-to-$250; the pricier repairs — pan, pump, refrigerant — run from about $150 to $1,600. Here's the national range for each, with the actual quote coming from the contractor after they read the system:
| Fix | Typical range |
|---|---|
| Drain-line clearing | $0–$250 |
| Condensate pump | $150–$400 |
| Drain pan replacement | $150–$600 |
| Refrigerant leak find + recharge | $225–$1,600 |
Full part-by-part pricing is on AC repair cost, and the visit fee itself on HVAC service call cost.
How do you stop the leak from coming back?
Leaks are mostly a maintenance failure, so prevention is simple: flush the drain line with a cup of vinegar every three to six months, change the filter monthly to quarterly so the coil never freezes, and book an annual tune-up that clears the line, checks the pan, and confirms the refrigerant charge. A clean-out access fitting makes the vinegar flush a two-minute job.
Frequently asked questions
Is it normal for an AC to leak water?
A little condensation dripping from the outdoor end of the drain line is normal. Water pooling indoors or around the indoor unit is not — it almost always means a clogged drain line, a frozen coil, or a cracked pan.
Why does my AC leak water only when it's turned off?
That's the signature of a frozen evaporator coil. While the unit runs with restricted airflow or low refrigerant, ice builds on the coil; when you shut it off, the ice melts faster than the drain can handle and overflows.
Can I run my AC while it's leaking water?
No. Running it worsens the water damage and invites mold, and if the cause is a frozen coil you risk the compressor. Turn it off, fix the drainage, then run it again.
Why is my AC leaking water from the ceiling or the bottom?
A ceiling stain under an attic unit, or water at the base of an indoor unit, both point to the condensate not draining — a clogged line, an overflowing or cracked pan, or a failed pump. Clear the line first, then inspect the pan.
Does a leaking AC mean I need a new unit?
Almost never. The most common cause is a clogged drain line, which is a cheap or free fix. Only a badly corroded system or a major refrigerant leak on an old unit pushes the conversation toward replacement.
Can low refrigerant make my AC leak water?
Yes, indirectly. Low refrigerant freezes the coil, and the melting ice leaks. Because low charge means a leak, this one needs a licensed technician, not just a drain-line flush.
How often should I flush the drain line?
Every three to six months. Pour a cup of vinegar down the drain line to kill the algae that causes clogs — it's the single most effective thing you can do to prevent leaks.