Central air conditioners produce condensation as a normal part of cooling humid air, and that water is supposed to drain away through a dedicated condensate line, out of sight. When you actually see water pooling near the indoor unit or dripping from the ceiling below an attic-mounted system, something in that drainage path isn't working the way it should.
A clogged condensate drain line
This is by far the most common cause. Algae, dust, and debris build up inside the drain line over time, and once it's blocked, condensation backs up and overflows instead of draining outside. It's also one of the most preventable causes, a seasonal tune-up typically includes flushing this line before it becomes a problem.
A full or malfunctioning condensate pump
Systems where gravity can't drain the condensate line naturally (often in a basement or a unit installed below the drain point) rely on a small pump to move the water out. If that pump fails or gets overwhelmed, water backs up right at the unit.
A frozen evaporator coil that's thawing
If the coil froze up due to restricted airflow or low refrigerant, the water you're seeing might actually be that ice melting off, producing more water than the drain system is designed to handle at once. If this is the cause, the leak is really a symptom of a separate airflow or refrigerant issue that needs its own diagnostic.
A cracked or disconnected drain pan
The drain pan underneath the indoor unit catches condensation before it reaches the drain line. Older pans can crack or corrode over time, and even a small crack is enough to let water escape before it ever makes it into the drain system.
Improper installation or a unit that's not level
If the indoor unit or drain pan wasn't installed level, water can pool on one side and overflow rather than draining evenly. This is less common with an experienced install, but it's worth mentioning if the leak started right after a new installation rather than developing gradually.
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