AC Leaking Water in Attic

The main 3/4-inch PVC drain line is clogged with algae, mold, or dust buildup. Water backs up into the primary pan, overflows into the secondary pan, and eventually drips through the ceiling.

Locate the AC unit in the attic. Find the PVC pipe leading away from the unit. Trace it to where it exits (usually outside soffit). No water exiting? Clogged.

Attic units often use a condensate pump to push water down/out. Failed pump = water accumulates in the primary pan until it overflows.

Look for a small plastic box with a tube exiting it near the AC. Lift the lid — if there's water sitting in it, the pump should have run. Test by pouring water in and listening for pump activation.

Older units develop pinholes or rust-through in the secondary pan beneath the air handler. Even modest overflow becomes a leak.

Visual inspection of the auxiliary pan (the one under the unit). Look for rust streaks, visible cracks, or water trails along seams.

Coil froze (low refrigerant, dirty filter, restricted airflow), then thawed all at once. The drain pan capacity is overwhelmed by the volume of melt water and overflows.

Did the AC recently stop blowing cold? Is there visible ice on the suction line? Did the leak start hours AFTER the AC seemed to malfunction?

The safety float switch is supposed to shut off the AC when water rises in the pan. If the switch failed open (stuck down), water keeps rising past the danger point.

Test by lifting the float manually with the AC running — it should immediately kill power to the unit. If the system keeps running, switch is bad.

PVC drain pipe has come loose from the unit fitting, or a slip joint has separated. Water exits the wrong place.

Trace the entire drain line. Look for separations, especially at slip joints or after recent service.