Air conditioners are supposed to drain the moisture they pull from the air to the outside. When that drain clogs, the water backs up and overflows inside — often from an attic unit, straight into the ceiling below.
Why your AC is leaking water inside
- Clogged condensate drain line — algae, mold, and mineral scale block the line so water backs up and overflows. The #1 cause in Tucson.
- Full or cracked drain pan — the pan under the coil rusts through or overflows when the line is blocked.
- Frozen evaporator coil — a dirty filter or low refrigerant freezes the coil; when it thaws, it dumps more water than the pan can hold.
- Dirty air filter — restricts airflow and contributes to coil freezing.
Why it's so common in a Tucson summer
Tucson air conditioners run nearly nonstop for months, pulling humidity all day and producing a constant stream of condensate. That continuous moisture, plus warm attic temperatures, is ideal for algae growth inside the drain line — and the area's hard water adds mineral scale. The result is a drain line that clogs and overflows right when the AC is working hardest.
What to do right now
- Turn the AC off at the thermostat to stop more condensate from forming.
- Find the source — check the indoor air handler, the drain pan, and any ceiling stain below an attic unit.
- Move valuables away and put down towels; stay clear of a sagging ceiling.
- Photograph the damage for insurance, then get the water dried before it spreads.
Attic units and ceiling damage
Many Tucson homes have the air handler in the attic, so a condensate overflow runs straight down into the ceiling and walls. By the time a stain appears, insulation and framing above are already wet — which is why drying the cavity, not just wiping the surface, is what prevents mold. A typical condensate-overflow cleanup runs $400–$2,000 depending on how far the water spread.
Preventing the next leak
Clear and flush the condensate drain line at the start of cooling season, change the air filter regularly, and have the system serviced annually. Most condensate overflows are simple clogs that routine maintenance would have prevented.
Common questions
FAQ
Why is my AC leaking water inside the house?
Almost always because the condensate drain — the line that carries away the moisture your AC pulls from the air — is clogged, so the water backs up and overflows. Other causes are a cracked or overflowing drain pan and a frozen evaporator coil (often from a dirty filter). In Tucson, algae and mineral clogs in the drain line are the most common culprit.
How do I stop my AC from leaking water?
Turn the AC off at the thermostat to stop producing condensate, then locate the source — usually a clogged condensate drain line or full drain pan at the indoor air handler. Clearing the drain line (and changing a dirty filter) resolves most cases. If water has reached a ceiling or walls, get it dried out before mold develops.
Can an AC leak cause ceiling damage?
Yes — very often in Tucson, because many homes have the air handler in the attic. When the condensate drain overflows, the water runs straight down into the ceiling and walls below, leaving stains, sagging, and wet insulation. The visible damage usually appears after the cavity above is already soaked.
My AC condensate drain is clogged — what do I do?
Turn off the AC, then clear the line. Many homeowners clear minor clogs by attaching a wet/dry vacuum to the outdoor end of the drain line, but a stubborn algae or scale clog, or a unit that's already overflowed into the ceiling, is worth a professional visit — plus drying any water damage the overflow caused.
Does an AC leak cause mold?
It can. A condensate overflow soaks porous materials — drywall, ceiling cavity, insulation — and mold can begin within 24–48 hours, especially in Tucson's summer heat. Standing water in the drain pan and damp ductwork can also grow mold, which is why clearing the clog and drying the affected area both matter.
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