Why is my AC leaking water inside the house?
A leaking AC means coil water can't reach the drain, and our $79 trip charge is waived when you approve the repair. Common causes are a clogged trap or line, a failed condensate pump, a frozen coil or a cracked pan. Turn cooling off and keep water off the furnace.
Key points
- A trickle at the end of the drain line, or sweat on the copper line outside, is normal. Water on the floor inside is not.
- Most inside leaks start at the coil's drain: a slimed trap or line, a failed pump, or a pan that's cracked or rusted through.
- A frozen coil sheds more water than the pan can hold when it melts. Fix the filter, airflow or refrigerant problem behind it.
- A float switch that shut the AC off did its job. Never bypass it.
- EPA advises drying water-damaged areas within 24–48 hours to prevent mold.
Water around the furnace or under the coil box, rust streaks down the cabinet, or a pump that is full and silent all say the path between the coil and the floor drain has failed somewhere, and the break is usually at the trap, the pump or a coil that froze and is now thawing.
Some water is supposed to be there, though, so start by sorting normal from not.
Is it normal for a central AC to drip water?
Every central AC makes water. Trane puts it plainly: as house air passes through the evaporator coil, the coil absorbs heat and water from it, and the condensed water leaves through a separate drain. On a humid Minnesota afternoon that drain carries a steady trickle.
Normal:
- A trickle at the end of the drain line, at a floor drain, a laundry tub, a condensate pump or a pipe through the wall
- A condensate pump that kicks on for a few seconds every so often
- Condensation dripping off the cold copper line and its valves at the outdoor unit on a muggy day
Not normal:
- Water on the floor around the furnace or under the coil box
- Water inside the furnace cabinet, or rust streaks down its sides
- A pump that's full and silent, or one that never stops
- A stain on a ceiling below an attic or closet unit, or water down the wall under a ductless head
Why is water dripping from the AC outdoor unit?
The outdoor unit of a central AC makes very little water of its own. What you usually see is sweat dripping off the cold copper line and its valves on a muggy day, or the trickle from the condensate line that ends near the house. Both are normal. Water running out of the cabinet itself, or a wet patch under the unit on a dry day, is worth a look.
A heat pump is different in winter. When frost builds on the outdoor coil, the unit switches into defrost, melts the frost and drips water, sometimes with a cloud of steam. That is normal and passes in several minutes. Call if the unit stays buried in ice, or the ice isn't clearing between defrost cycles. If the AC drips inside and the line is iced up, our guide to why an AC freezes up covers it.
Why is my mini-split leaking water inside the house?
A ductless head drains the same way a central coil does, through a small hose out the back. When that hose can't carry the water, it comes out the front of the head and runs down the wall. The usual causes:
- A clogged or kinked drain hose. Slime, dirt or a pinched hose keeps water from leaving.
- A head that is out of level. If it tilts away from the drain side, water spills over the pan edge.
- A dirty filter or coil. Restricted airflow can ice the coil, and the meltwater overruns the pan.
- A failed condensate pump, on heads that lift water to a drain.
Turn the head off, put a towel under it, and rinse the filter. If the leak returns, it needs a technician; our ductless mini-split service covers drain cleaning and re-leveling.
What to do right now
- Turn cooling off at the thermostat. Leave the fan off for now so the coil stops making water.
- Protect the furnace. If water is on or under the furnace, switch it off at its service switch, but only if you can reach the switch without standing in water. If water has reached an outlet, a cord or the electrical panel, stay out of it and call.
- Soak it up. Towels, a mop or a wet/dry vacuum, and move stored boxes off the floor. EPA advises drying water-damaged areas and items within 24–48 hours to prevent mold.
- Find where it starts. Follow the water uphill: coil box, trap, drain line, pump. The table below matches what you find to the usual cause.
- Clear the drain. Most leaks are a slimed-up trap or line. Our guide to clearing a clogged condensate drain walks through flushing the cleanout and vacuuming the line from its far end.
- If you find ice, let it melt. Cooling off, fan set to On, towels around the furnace. It can take several hours.
- Restart and watch. Run cooling for 20 minutes. You want a steady trickle at the end of the line and nothing collecting under the coil.
If the AC went dead along with the leak, a float switch in the pan, on the drain line or in the pump probably shut it off on purpose, before the floor filled. It usually resets once the water drains. Never bypass one to get the AC running. If your system kept running while water spilled, it has no switch or a failed one, and it's worth adding one. An attic or upstairs-closet air handler should always have a secondary pan with its own switch or drain, because water up there has nowhere to go but through a ceiling.
Where the water is, and what it usually means
| Where you find water | Usual cause | What to do | Who handles it |
|---|---|---|---|
| Floor around the furnace, AC running | Clogged trap or drain line | Cooling off, flush or vacuum the line | You |
| Around the condensate pump | Stuck float, plugged check valve or a worn-out pump | Rinse the reservoir and float, test with water | You, or a technician for a new pump |
| Ice on the big copper line, then water | Frozen coil: dirty filter, weak blower or low refrigerant | Cooling off, fan On to thaw, new filter | A technician if it refreezes |
| Inside the furnace cabinet | Cracked or rusted coil pan, or an overflowing pan | Furnace off at its switch | A technician |
| Drips along the copper line or coil box | Sweating where insulation is missing | Towels now, insulation later | You or a technician |
| Ceiling stain below an attic unit | Primary drain clogged, secondary pan full | Cooling off now | A technician, right away |
| Wall under a ductless head | Clogged or kinked head drain, or a head out of level | Turn the head off | A technician |
| Near the furnace with the AC off | Humidifier, furnace condensate or the water heater | Check those first | You, then whoever owns the source |
When it isn't the drain
A frozen coil
A Department of Energy field guide notes that a system low on refrigerant can form ice on the evaporator coil, and that a coil fouled with dirt cuts airflow until it freezes over. The ice can build out past the edges of the pan, and when the system shuts off it can melt faster than the drain can carry it. Replace the filter and make sure the blower is moving air. If the coil refreezes within a day, the cause is refrigerant or airflow that needs a technician; our guides to an AC running but not cooling and a leaking evaporator coil cover both.
A cracked or rusted pan
Many older coils sat in steel pans that can rust through, and plastic pans can crack with age. Water then drips inside the coil box instead of reaching the drain, and on a typical basement furnace it lands on the furnace below. Some pans can be replaced by themselves; on other coils the pan is part of the assembly and the fix is a coil.
Sweating metal
Cold surfaces in a humid basement pull water out of the air: a copper line with split insulation, the coil box, the supply plenum, bare cold water pipes. It looks like a leak but isn't. EPA's advice is to insulate cold surfaces such as cold water pipes and keep indoor humidity below 60 percent, ideally 30 to 50. A basement that stays damp all summer may need a whole-house dehumidifier.
The humidifier or the furnace
Many Minnesota furnaces carry a whole-home humidifier, and a stuck water valve or plugged drain can dribble water down the furnace in July. For heating-season leaks, see why a furnace leaks water.
How much does it cost to fix an AC water leak?
For scale, HomeGuide's typical national ranges are $75–$250 to clear a condensate drain line and $100–$450 to replace a condensate pump. If a rusted or cracked pan means a new coil, HomeGuide puts evaporator coil replacement at $2,500–$4,500 out of warranty and $1,000–$2,500 with the coil under warranty. Those are national figures, not our prices, and our Minneapolis HVAC cost page covers the condensate pumps common in low basements far from a floor drain.
With us, you get a written flat-rate price before any work starts. A spring AC tune-up is $129, or $219 with the furnace, and is the easiest time to ask for the drain line and the pan under the coil to be looked at before a slow drain overflows.
When should you call a technician about an AC leak?
- Water inside the furnace cabinet or on the control board
- A stain or drip on a ceiling below an attic or closet unit
- Ice that comes back within a day of thawing
- A pump that won't run after you've cleaned the float
- A leak that returns within days of clearing the drain
- A musty smell with visible growth in the pan or coil box. EPA advises against running an HVAC system you suspect is contaminated with mold, since it can spread mold through the house.
If water is reaching the furnace, call 612-429-3465; we're open 7am–9pm every day. The price is the same from AC repair in Minneapolis to AC repair in Saint Paul.
Common questions about cooling
Can I keep running my AC while it's leaking?
Not until you know why. A float switch that shut it off is doing its job and stays off until the drain clears. If it is still running and spilling, every hour puts more water near the furnace wiring and the floor. Turn cooling off, clear what you can, and restart once water drains again.
Why does my AC leak only on the most humid days?
Because that's when the coil makes the most water. A drain partly blocked with slime, or one that sags or runs too flat, can keep up on an ordinary day and back up on a muggy one, and a condensate pump that is wearing out does the same. If leaks line up with sticky weather, have the trap, slope and pump checked.
Is water around the outdoor AC unit a problem?
Usually not. The outdoor unit makes very little water of its own. What you see is condensation dripping from the cold copper line and valves on a muggy day, or the trickle from the condensate line that ends near the house. Water running out of the cabinet itself, or a wet patch under the unit on a dry day, is worth a technician's look.
How much does it cost to fix an AC water leak?
HomeGuide's national ranges are $75–$250 to clear a condensate drain line and $100–$450 to replace a condensate pump, and $2,500–$4,500 for an evaporator coil out of warranty. Those are national figures, not our prices. With us you get a written flat-rate price before any work starts.
Sources
- U.S. Environmental Protection Agency epa.gov
- Trane manufacturer documentation trane.com
- HomeGuide cost guides (2026 editions) homeguide.com