AC Condensate Line Overflow in Arizona Homes

Why do AC condensate lines overflow?

AC condensate lines overflow when the drain line clogs or the drain pan fails, so water from the cooling coil has nowhere to go. As your air conditioner cools, it pulls moisture out of the air. That water drips into a drain pan and flows out through a PVC condensate line. In the East Valley, AC systems run most of the year, so the line carries a lot of water and has a lot of time to clog.

Common causes

• Algae and slime growing inside the line
• Dust and debris washed off the coil
• Mineral scale from hard water
• A rusted or cracked drain pan, common on older systems
• A frozen coil that melts all at once and overwhelms the pan
• Poor slope or a disconnected line, sometimes from original installation

Warning signs of an overflow

1. Water around the indoor unit, in the AC closet or on the garage floor
2. A ceiling stain below an attic air handler
3. Water in the secondary (emergency) drain pan
4. The AC shutting off unexpectedly, which can mean a float switch tripped
5. A musty smell when the system starts
6. Water dripping from the secondary drain line outlet, often over a window, which signals the primary line is blocked

How to clear a clogged condensate line

If your system has an accessible cleanout, often a capped T-fitting near the unit:

1. Turn off the AC at the thermostat and breaker.
2. Remove water from the drain pan with towels or a wet vac.
3. Use a wet vac on the outdoor end of the line to pull out the clog.
4. Flush the line through the cleanout with water or a cup of distilled white vinegar.
5. Restart the AC and confirm water drains outside.

If the line keeps clogging, the pan is rusted, or there is no float switch, call an HVAC contractor. We repair the water damage; the HVAC contractor fixes the system.

Preventing AC water damage

• Flush the condensate line at the start of the cooling season.
• Make sure a float switch is installed and working.
• Replace rusted drain pans before they fail.
• Change air filters on schedule, since dirty filters can freeze the coil.
• Look in the AC closet or attic platform a few times a year.

When AC water reaches the ceiling

A soaked ceiling below an attic unit needs prompt drying. Wet insulation holds water against the drywall, and the attic is warm, which favors mold. Keep people out of a room with a sagging ceiling and call for help. Our guide on how fast mold grows explains why speed matters.