Why Is Air Conditioner Leaking Water? (7 Causes & Fixes)

Water dripping from your air conditioner is one of the most common AC problems — and one of the most alarming to discover. The good news is that most causes are straightforward to diagnose and fix yourself. Here's what's causing it and how to stop it.

Why Does an AC Produce Water in the First Place?

As your AC cools the air, it also removes humidity. Warm, moist air passes over the cold evaporator coil, and moisture condenses on the coil — just like water droplets form on a cold glass. This condensate drips into a drain pan and flows out through the drain line. When something goes wrong with this process, water leaks inside.

1. Clogged Condensate Drain Line

Most common cause. Algae, mold, and sludge build up in the drain line over time, blocking the flow of condensate. Water backs up into the drain pan and overflows inside.

Fix: Clear the drain line with AC drain line cleaner and prevent future buildup with condensate pan tablets. See our full guide on how to clean the AC drain line.

2. Dirty Air Filter

A clogged filter restricts airflow over the evaporator coil. Without enough warm air flowing over it, the coil gets too cold and freezes. When the ice melts, it produces more water than the drain pan can handle, causing overflow.

Fix: Replace or clean the filter immediately. Use Amazon Basics MERV 8 filters and replace every 60–90 days.

3. Frozen Evaporator Coil

If the evaporator coil freezes (from restricted airflow, low refrigerant, or running the AC in very cold weather), the ice melts when the unit cycles off, producing a large amount of water at once that overwhelms the drain pan.

Fix: Turn the AC off and let it thaw completely (2–4 hours). Run the fan only to speed thawing. Then address the root cause — usually a dirty filter or low refrigerant. See our guide on why your AC is freezing up.

4. Disconnected or Cracked Drain Pan

The drain pan under the evaporator coil can crack over time (especially in older units) or become misaligned, allowing water to drip past it.

Fix: Inspect the drain pan. Small cracks can be sealed with waterproof epoxy as a temporary fix. A severely damaged pan should be replaced — a technician can do this during a service visit.

5. Improper Installation Angle

Window AC units must be installed with a slight tilt toward the outside so condensate drains outward. If the unit is level or tilted inward, water drains inside instead of out.

Fix: Reinstall the window unit with a 1–2 degree tilt toward the outside. Use a level to check and adjust the mounting brackets.

6. Low Refrigerant

Low refrigerant causes the evaporator coil to run too cold and freeze. When it thaws, excess water overflows the drain pan.

Fix: Use a refrigerant leak detector to check for leaks. Refrigerant recharging must be done by a licensed HVAC technician.

7. High Humidity

In extremely humid conditions, the AC produces more condensate than usual. If the drain line is even partially restricted, it may not keep up with the increased volume of water.

Fix: Flush the drain line proactively before humid season. Add condensate pan tablets to prevent algae growth that could cause a blockage.

Quick Diagnostic Guide

When to Call a Technician

Call a professional if: the leak continues after clearing the drain line and replacing the filter, you suspect a refrigerant leak, or the drain pan is cracked and needs replacement.

Most AC water leaks are caused by a clogged drain line or dirty filter — both fixable in under an hour. Address it promptly to prevent water damage to walls, ceilings, and flooring.