Air Conditioner Leaking Water? 5 Common Causes & How to Fix Them

An air conditioner is supposed to make you comfortable, but seeing a puddle of water forming on your floor or ceiling is anything but. While a leaking AC unit is alarming and can cause serious water damage, it’s a very common problem.

The good news is that the single most frequent cause of an AC leaking water inside the house is a simple issue that a handy homeowner can often fix themselves.

This guide will walk you through the most common causes, starting with the easiest DIY fix, and help you determine when it’s time to call a professional.

First, a Quick Science Lesson: Why Does an AC Create Water?

Your air conditioner works like a cold glass of iced tea on a humid day. As warm, humid air from your home blows over the frigid evaporator coils inside your AC unit, the moisture in the air condenses into water—just like water droplets forming on the outside of the cold glass.

This process is completely normal. A properly working AC is designed to collect this condensation in a drain pan and safely channel it outside your home through a PVC pipe called a condensate drain line.

A leak happens when something interrupts this drainage process.

The #1 Cause: A Clogged Condensate Drain Line

This is, by far, the most common reason for an AC leaking water inside your home. Over time, the dark, damp environment of the drain line becomes a breeding ground for algae, mold, and sludge. This gunk can form a clog, causing the water in the drain pan to back up and overflow, spilling into your home.

How to Fix It (The DIY Method): If you’re comfortable with some basic DIY, you can often clear this clog yourself.

1. Turn Off the Power: First, turn off the power to your AC system at the thermostat and at the circuit breaker.
2. Locate the Drain Line: Find the white PVC pipe coming out of your indoor air handler unit. Near the unit, you should see a T-shaped pipe with a cap on top. This is the access port.
3. Clear the Clog:
   • Remove the cap from the access port.
   • Pour a cup of distilled white vinegar into the pipe. Let it sit for 30-60 minutes to dissolve the gunk.
   • Afterward, flush the line by pouring a few cups of hot water down the pipe.
   • For tougher clogs, you can use a wet/dry shop vacuum. Connect the vacuum’s hose to the end of the drain line outside your house and create a tight seal with your hand or a rag. Let the vacuum run for a few minutes to suck the clog out.
4. Restore Power: Once the line is clear, you can turn the power back on.

Other Common Causes (And When to Call a Pro)

If a clogged drain line isn’t the issue, the problem is likely more technical and will require a professional.

2. Dirty Air Filter

Yes, the same culprit from our “AC not blowing cold” guide. A severely clogged air filter restricts airflow over the evaporator coils. This can cause the coils to get too cold and freeze into a block of ice. When that ice melts, the drain pan can’t handle the sudden large volume of water, causing it to overflow. Solution: Check and replace your air filter monthly.

3. Low Refrigerant

Low refrigerant levels also cause the evaporator coils to freeze. As with a dirty filter, the melting ice overwhelms the drain pan. You’ll often see ice on the coils themselves or on the copper refrigerant lines. This indicates a refrigerant leak, which requires a licensed HVAC technician to repair and recharge the system.

4. Cracked Drain Pan

With older AC units, the drain pan itself can become rusted, damaged, or cracked with age. If the pan is compromised, water will leak out even if the drain line is perfectly clear. Solution: The drain pan will need to be replaced by a professional.

5. Broken Condensate Pump

If your indoor AC unit is located in a basement or attic below the level where the drain line exits your house, your system will have a small device called a condensate pump. This pump’s job is to collect the water and actively pump it uphill and outside. If this pump fails, the water will back up and overflow. Solution: The pump needs to be repaired or replaced by a technician.

The Bottom Line

If you see water coming from your indoor AC unit, the first and most important step is to check for a clogged condensate drain line. If you can’t clear the clog yourself or if you see signs of a more serious issue like frozen coils, turn off your system to prevent water damage and call a professional for help.