AC Leaking Water Inside? Causes and How to Fix It
Water around the indoor unit, a dripping ceiling or a full drain pan.
By Mark Curant·Updated
Most likely causes
- A clogged condensate drain line (algae and dirt), the most common cause by far
- A frozen coil melting faster than the drain can carry it away
- A failed condensate pump
- A cracked or rusted drain pan
- A drain line that has come loose
Before you open anything
Turn the system off at the thermostat, then switch off power at the breaker and at the disconnect beside the outdoor unit. Never touch the capacitor, even with the power off: it can hold a dangerous charge. Refrigerant work is for licensed technicians only. Reset a tripped breaker once; if it trips again, leave it off.
Check these first (free, 5 minutes)
- Turn the system off at the thermostat to stop more water being produced.
- Look for ice on the indoor coil or copper lines. If there is any, the coil is freezing.
- Check the drain pan under the indoor unit for standing water.
- If you have a condensate pump (a small box with a tube, near the unit), check whether it's full.
Causes, signs and repair costs
Clogged drain line
DIY or proStanding water in the pan, overflow, system shut off by a float switch
Typical cost: $10–$20 DIY, $75–$200 pro
Frozen coil melting
DIY or proIce on the coil or lines, weak airflow
Typical cost: Depends on the cause
See: AC frozen up →Failed condensate pump
DIY or proPump reservoir full, pump doesn't switch on, water around it
Typical cost: $150–$400
Cracked or rusted drain pan
ProDrain clear but water still drips from under the unit
Typical cost: $200–$600
Loose or disconnected drain line
DIYWater at a joint in the PVC line
Typical cost: $0–$20
| Cause | Signs | Who fixes it | Typical cost |
|---|---|---|---|
| Clogged drain line | Standing water in the pan, overflow, system shut off by a float switch | DIY or pro | $10–$20 DIY, $75–$200 pro |
| Frozen coil meltingSee: AC frozen up → | Ice on the coil or lines, weak airflow | DIY or pro | Depends on the cause |
| Failed condensate pump | Pump reservoir full, pump doesn't switch on, water around it | DIY or pro | $150–$400 |
| Cracked or rusted drain pan | Drain clear but water still drips from under the unit | Pro | $200–$600 |
| Loose or disconnected drain line | Water at a joint in the PVC line | DIY | $0–$20 |
Typical U.S. installed prices in 2026. Most repairs also carry a service call fee of $75–$200, often credited toward the repair. See AC repair costs in 2026 for the full list.
Step by step
- 1
Turn the system off and dry up
Switch off cooling at the thermostat and turn off power to the indoor unit. Soak up water around the unit, and use a wet/dry vacuum to empty the drain pan.
- 2
Find the drain line
It's usually a 3/4-inch PVC pipe leaving the indoor unit, often with a T-shaped fitting and a cap (the cleanout) near the unit. Follow it to where it ends outside or at a floor drain.
- 3
Clear the clog from outside
Hold a wet/dry vacuum hose over the outside end of the line, seal it with your hand or a rag, and run it for a minute or two. You'll often pull out a plug of slime.
- 4
Flush from the cleanout
Remove the cap and pour in a cup of distilled white vinegar, then some water to check it flows freely. Check your unit's manual first: a few manufacturers recommend against certain cleaners.
- 5
Check the pump and switch
If you have a condensate pump, pour a little water into its reservoir: it should switch on and pump it away. Restore power, set the thermostat to Cool, and check the pan stays dry after an hour.
Call a technician if
- Water keeps coming back after clearing the drain
- Water is dripping through a ceiling (an attic unit's pan may be overflowing or rusted through)
- The condensate pump doesn't switch on
- The coil is freezing
Red flags on a quote
- A new coil or system for a leak that a drain clearing would fix
- Drain clearing priced well above $200 without other work
Facing an expensive repair on an older system? Run it through the repair vs replace calculator, or read the $5,000 rule.
Frequently asked questions
Why is my AC leaking water inside the house?
Air conditioners pull moisture out of the air and drain it away through a condensate line. If that line clogs with algae and dirt, the water backs up and overflows the drain pan. That's the cause most of the time. A frozen coil, a failed condensate pump or a cracked pan are the other usual suspects.
How do I unclog my AC drain line?
Turn off the system, then use a wet/dry vacuum on the outside end of the drain line for a minute or two to pull out the clog. Then pour a cup of distilled white vinegar into the cleanout near the indoor unit, followed by water to check it flows.
How often should I clean the AC drain line?
Pour vinegar into the cleanout every month or two during the cooling season. In hot, humid places where the AC runs most of the year, algae grows fast and monthly is worth it.
Related problems
AC frozen up
Ice on the copper lines or indoor coil, weak airflow, water as it melts.
AC won't turn on
Nothing happens when you lower the thermostat: no fan, no outdoor unit.
AC blowing warm air
The fan runs but the air coming out of the vents is warm or barely cool.
Fixed it? Check what it costs to run
If your system is old enough to keep breaking, compare its running cost with a new one before the next repair.
Open the SEER savings calculator