Short answer
An attic AC unit leaks through the ceiling when its condensate drain line clogs, the drain pan rusts through, or the float switch fails. Turn the AC off at the thermostat, catch the drip, and have both the HVAC system and the wet ceiling checked.How condensate works
An air handler pulls a lot of water out of indoor air in summer. It drains through a small PVC line, usually to the outside or a plumbing drain. If that line clogs with algae or debris, water backs into the pan.
What to check
Some checks are safe for most homeowners.
- Is water dripping from the outside condensate outlet?
- Is the secondary drain (often over a window) dripping? That means the main line is clogged
- Does the attic pan have standing water?
What to shut off
Turn the AC off at the thermostat to stop producing condensate. Put a bucket and tarp under the leak, and stay out from under sagging drywall.
Fixing the ceiling
Wet insulation above the ceiling is usually removed. Lightly damp drywall can sometimes be dried in place; stained, soft or sagging sections are replaced and textured to match.
Questions
How often should the condensate line be cleaned?
At least once a year during AC maintenance, and more often if you've had clogs. Many techs flush the line at every service visit in the Valley.
What does a float switch do?
It shuts off the AC when water rises in the drain pan or line, preventing overflow. If it's missing or stuck, the pan can overflow into the ceiling.
This guide is general information for Arizona homeowners, not a substitute for an on-site assessment or your insurance policy wording.