Why Is My AC Leaking Water Inside?

Where That Water Comes From

On a sticky July afternoon in Philadelphia or South Jersey, your air conditioner can pull several gallons of water out of the air in a single day. All that moisture condenses on the evaporator coil, drips into a drain pan, and exits through a condensate line. When you find a puddle under the indoor unit, it means something in that path has failed — not that the system is "sweating" normally.

The Five Most Common Causes

• A clogged condensate drain line. Algae and sludge build up in the line over a humid Northeast summer until water backs up into the pan and overflows. This is the cause we find most often.
• A dirty air filter. Restricted airflow can freeze the evaporator coil; when the ice melts, it releases more water than the pan can handle.
• A cracked or rusted drain pan. On systems 15 years or older, the pan itself may have corroded through.
• A failed condensate pump. Many Philly rowhome basements sit below the level of any drain, so the system relies on a small pump. When it dies, water has nowhere to go.
• A low refrigerant charge. Like a dirty filter, low refrigerant can ice the coil and flood the pan when it thaws.

What You Can Safely Do Yourself

Turn the system off at the thermostat to stop the leak from growing, then soak up standing water so it doesn't damage flooring or drywall. Replace the air filter if it's dirty, and check that the condensate line isn't kinked or disconnected. If you can reach the line's outdoor outlet, a wet/dry vacuum held over the end for a minute will often pull the clog out.

When to Call a Pro

Call an air conditioning professional if water has reached electrical components, if the coil is visibly iced over, if you see ceiling stains under an attic air handler, or if the leak returns after you've cleared the line. Diagnosing a refrigerant issue requires certified handling and proper gauges — it is never a DIY job, and running an iced-up system can destroy the compressor.

One more thing: a leaking AC and a clammy house often share a root cause. If your home feels damp even when the system runs, read our guide on why your house is so humid with the AC on.