Finding water around your furnace/AC or dripping from a ceiling vent is alarming — and left alone, it can cause mold and water damage. The good news: most AC water leaks come down to a few common, fixable causes.
1. A clogged condensate drain line
This is the #1 cause. As your AC cools, it pulls moisture from the air, which drains away through a small PVC line. Over time that line clogs with algae and gunk, water backs up, and it overflows the pan. A wet/dry vac on the drain outlet can sometimes clear it; a stubborn clog needs a pro.
2. A full or rusted drain pan
The pan under your indoor coil catches condensation. If it's cracked or rusted through (common on older systems), water leaks straight onto the floor.
3. A frozen evaporator coil
If the coil freezes and then melts, the runoff overwhelms the drain pan. Frozen coils usually come from a dirty filter, low refrigerant, or restricted airflow. If you see ice on the unit, shut the AC off and let it thaw — and read why this happens in our guide to an AC that runs but won't cool.
4. A dirty air filter
A filthy filter restricts airflow, which can freeze the coil. Checking your filter monthly prevents a surprising number of problems.
5. A condensate pump failure
Homes where the AC sits in a basement often use a small pump to push condensation out. If the pump fails, water has nowhere to go.
What you can do right now
- Turn the AC off to stop more water and prevent damage.
- Check and replace a dirty air filter.
- Look for ice on the unit — if present, let it fully thaw.
- Clear standing water before it damages flooring.
When to call us
If the drain line stays clogged, the pan is damaged, or the coil keeps freezing, it's time for a technician. Thermo Master handles AC repair throughout Palatine and the northwest suburbs — get in touch and we'll find the source and stop the leak for good.