Air Conditioner Leaking Water: Why It Happens and How to Fix It
An air conditioner leaking water inside your home almost always comes down to one thing: the water it normally removes from your air isn’t draining where it should.
Your AC pulls several gallons of moisture out of the air on a humid day. That water collects in a pan and exits through a drain line. When that path clogs, freezes or tilts the wrong way, the water finds another route, usually your ceiling or floor.
The good news is that the most common cause is something you can fix yourself in about 20 minutes. Here’s how to work out which situation you’re in.
First: Turn the System Off
Before troubleshooting, shut the AC off at the thermostat.
Two reasons. Running the system keeps producing condensate, which means more water pooling while you work. And if the leak is near electrical components, which it often is inside an air handler, continuing to run it is a genuine hazard.
Place towels or a shallow pan to catch what’s still dripping, and let’s narrow down the cause.
Where Is the Water Coming From?
Location tells you a lot.
| Where You See Water | Most Likely Cause |
|---|---|
| Around the indoor air handler | Clogged drain line or full drain pan |
| Dripping from ceiling vents | Duct condensation or overflowing pan above |
| Ceiling stain below an attic unit | Drain pan overflow, often clogged line |
| Around the outdoor unit | Usually normal (see below) |
| From a window unit, inside | Unit tilted wrong or clogged drain |
| Only after the system runs a while | Slow drain restriction |
| Water plus visible ice | Frozen coil that’s now thawing |
Symptom-Cause Table
| What You’re Seeing | Likely Cause | Fix It Yourself? | Urgency |
|---|---|---|---|
| Steady drip near indoor unit | Clogged condensate drain line | Yes | 🟡 Soon |
| Water plus ice on the coil or lines | Frozen evaporator coil | Partly | 🟡 Shut it off now |
| Water only in high humidity | Undersized drain or heavy condensate load | Partly | 🟢 Monitor |
| Rusty or cracked pan visible | Failed drain pan | No | 🟡 Soon |
| Water near the air handler with a full pan | Clogged line or failed pump | Partly | 🟡 Soon |
| Damp insulation on ducts | Duct condensation | Partly | 🟢 Low |
| Water at outdoor unit only | Normal condensate discharge | No action | 🟢 Normal |
Cause 1: Clogged Condensate Drain Line
This is the cause in most cases, and it’s usually a DIY fix.
The drain line is a PVC pipe carrying condensate away from the indoor unit. It stays damp and dark, which makes it an ideal environment for algae and biological slime. Over a season or two, that buildup narrows the pipe until water can’t get through.
When the line clogs, the drain pan fills, and once it’s full the water goes over the edge.
How to confirm: look at the drain pan under the indoor unit. Standing water in the pan while the system runs means the line isn’t draining. Some systems have a clear section of line where you can see the blockage.
How to fix it:
- Turn the system off at the thermostat and the breaker.
- Find the access point on the drain line, usually a capped T-shaped fitting near the indoor unit.
- Remove the cap.
- Use a wet/dry vacuum at the outdoor end of the drain line to pull the clog out. Seal around the pipe with a rag for better suction and run it for a couple of minutes.
- Pour about a cup of distilled vinegar into the access point to kill remaining growth.
- Wait 30 minutes, then flush with water and confirm it drains freely.
- Replace the cap.
Prevention: flush the line with vinegar twice a year, or quarterly in humid climates. Our AC condensate drain line guide covers the system in more detail, and how to unclog an AC drain line walks through stubborn blockages.
Cause 2: Frozen Evaporator Coil
If you see ice along with water, this is your answer. The water is melting ice, and it’s coming off faster than the pan can handle.
A coil freezes when airflow across it drops too low or when refrigerant pressure is too low. Ice builds up, and when the system cycles off or you shut it down, all that ice melts at once, overwhelming the drain.
How to confirm: look for frost or ice on the copper refrigerant lines or the indoor coil. Water that appears suddenly in volume, rather than as a steady drip, points here.
What to do:
- Turn cooling off but set the fan to ON. This speeds thawing.
- Place towels and containers to catch meltwater.
- Wait. Full thaw takes 1 to 24 hours depending on buildup.
- Replace the air filter, since a clogged filter is the most common cause.
- Once thawed, restart cooling and watch whether ice returns.
If it freezes again within a day, the problem isn’t airflow. It’s most likely low refrigerant, which means a leak and a technician. Our guide on AC freezing up covers this in full.
Cause 3: Dirty Air Filter
A clogged filter is often the root cause behind a frozen coil, which is what leads to the water.
Restricted airflow means the evaporator coil gets colder than designed. Below freezing, condensation on the coil turns to ice instead of dripping into the pan. Then it melts all at once.
How to confirm: pull the filter and hold it to a light. If you can’t see through it, replace it.
What to do: replace the filter, thaw any ice, and check monthly during cooling season. Our air filter cleaning guide covers sizing and MERV ratings.
Cause 4: Damaged or Rusted Drain Pan
Drain pans corrode. On systems over 12 to 15 years old, rust holes or cracks are common, and water simply falls through.
How to confirm: inspect the pan with a flashlight. Look for rust, visible cracks, or water dripping from underneath rather than overflowing the edge.
What to do: this needs a technician. Pan replacement typically runs $200 to $600 depending on access, and on an aging system it’s worth asking about the condition of surrounding components while they’re in there.
Cause 5: Failed Condensate Pump
If your air handler sits in a basement or anywhere the drain can’t flow downhill, a small pump moves the water. When the pump fails, water backs up.
How to confirm: locate the pump near the indoor unit, usually a small box with a discharge tube. Listen for it running when the pan fills. If the pan is full and the pump is silent, it’s failed.
What to do: pump replacement runs $150 to $400 installed. Some models can be replaced by a confident DIYer, but it involves electrical connections and correct float switch setup.
Cause 6: Improper Installation or Slope
Drain lines need continuous downward slope. If a line sags, or was installed nearly level, water pools inside instead of flowing out. Over time, that standing water accelerates algae growth and clogging.
Window units have a similar problem. They’re designed to tilt slightly toward the outside so condensate drains out the back. Installed level or tilted inward, water runs into the room.
How to confirm: for central systems, look for visible sags in the drain line. For window units, use a level on the top of the unit; the outside edge should sit slightly lower.
What to do: window units can be re-shimmed yourself. Central system drain line correction is a technician job unless the sag is easily accessible.
Cause 7: Duct Condensation
Sometimes the water isn’t coming from the unit at all.
When cold air travels through ducts in a hot, humid attic or crawl space, moisture condenses on the outside of the duct, the same way a cold glass sweats. If duct insulation is damaged or missing, that condensation drips.
How to confirm: damp insulation on duct exteriors, water in areas away from the air handler, or drips that appear at duct joints.
What to do: repair or replace damaged duct insulation. Small sections are DIY-friendly with proper insulation wrap and foil tape.
When Water at the Outdoor Unit Is Normal
Worth clearing up, because it worries people unnecessarily.
Water pooling around your outdoor unit is usually normal. On humid days, condensate drips from the unit. In some systems, the outdoor unit also releases water during defrost cycles.
When it’s not normal: a large, persistent puddle that never dries, water when the system hasn’t run, or oily residue mixed with the water, which can indicate a refrigerant issue.
When to Call a Pro
- Water near electrical components in the air handler
- The leak returns after clearing the drain line
- You see ice repeatedly after thawing and changing the filter
- The drain pan is cracked or rusted through
- Water is damaging ceilings or walls
- You suspect a refrigerant problem, which is legally a professional job
Water damage compounds quickly. A slow ceiling leak that costs $250 to fix at the source can become a drywall and mold remediation project if left running for weeks.
What Repairs Typically Cost
| Repair | Typical Range |
|---|---|
| Drain line clearing (DIY) | $5 – $15 in supplies |
| Professional drain line clearing | $100 – $300 |
| Condensate pump replacement | $150 – $400 |
| Drain pan replacement | $200 – $600 |
| Duct insulation repair | $150 – $500 |
| Refrigerant leak repair | $500 – $1,500 |
Diagnostic fees of $75 to $150 apply to most service calls and are often waived if you approve the repair.
How to Prevent This
Nearly every cause on this list traces to maintenance.
- Flush the drain line with vinegar twice a year, quarterly in humid climates
- Change the filter every 1 to 3 months during cooling season
- Check the drain pan during seasonal maintenance for rust or standing water
- Have the coil cleaned annually, since a dirty coil contributes to freezing
- Watch for slow drips rather than waiting for visible damage
Our AC maintenance guide covers the full schedule.
Frequently Asked Questions
Why is my air conditioner leaking water inside?
The most common cause is a clogged condensate drain line. Algae and sludge build up in the line, water backs up in the drain pan, and once the pan fills it overflows. Other causes include a frozen evaporator coil melting, a rusted drain pan, or a failed condensate pump.
Is it dangerous if my AC is leaking water?
The water itself isn’t dangerous, but the consequences can be. Water near electrical components inside the air handler is a hazard, and prolonged leaking causes ceiling damage, wall damage and mold growth. Shut the system off and address it rather than letting it run.
Can I still run my AC if it’s leaking water?
You shouldn’t. Running the system produces more condensate, which means more water. If the leak involves a frozen coil, running it makes the ice worse. Turn cooling off, and if there’s ice, set the fan to ON to speed thawing.
How do I unclog an AC drain line?
Turn the system off, locate the access cap near the indoor unit, and use a wet/dry vacuum at the outdoor end of the line to pull the clog out. Then pour about a cup of distilled vinegar into the access point, wait 30 minutes, and flush with water.
How much does it cost to fix an AC water leak?
If it’s a clogged drain line you clear yourself, under $15 in supplies. Professional drain clearing runs $100 to $300. A failed condensate pump costs $150 to $400, and a rusted drain pan $200 to $600. Refrigerant-related causes run considerably higher.
Why is my AC leaking water only on humid days?
High humidity means your system removes far more moisture from the air, sometimes several gallons a day. A drain line that’s partially restricted may handle normal condensate but overflow when volume increases. It’s an early warning that the line needs clearing.
Should there be water around my outdoor AC unit?
Some water is normal, especially on humid days when condensate drips from the unit. A large persistent puddle that never dries, water when the system hasn’t run, or oily residue in the water are worth investigating.
Bottom Line
Turn the system off first, then look for ice. If there’s ice, thaw it and change the filter. If there’s no ice, the drain line is the most likely culprit, and clearing it with a wet/dry vacuum and vinegar takes about 20 minutes.
Call a technician if the leak returns after clearing the line, if you see rust or cracks in the drain pan, or if there’s water near electrical components. Water damage gets expensive faster than the repair does.