Water dripping from an indoor AC unit sometimes gets dismissed as a minor nuisance. It isn't — a properly functioning AC should never leak, and the underlying cause tends to get worse the longer it's left unaddressed.
A clogged condensate drain line
This is the most common cause by far. The thin drain line that carries condensation away from the indoor unit gets blocked by dust, algae, or debris over time, causing water to back up and overflow instead of draining outside.
Incorrect installation
If the indoor unit wasn't mounted with the correct slight tilt toward the drain outlet, water won't flow out properly regardless of how clean the drain line is. This is a common issue with units installed by less experienced technicians, and unfortunately requires reinstalling the unit correctly to fix.
A frozen evaporator coil
Low refrigerant or restricted airflow can cause the evaporator coil to ice up. When the unit is turned off (or the ice naturally melts during operation), that ice becomes water — often more than the drain system is designed to handle at once, causing overflow.
Why you shouldn't ignore it
- Water stains and mold growth on ceilings and walls near the unit
- Damage to flooring or furniture directly beneath the indoor unit
- Electrical risk if water reaches wiring inside the unit or nearby outlets
- The underlying cause (ice buildup, blocked drain) usually indicates a bigger problem that will worsen over time
If you notice dripping, it's worth having a technician inspect it promptly — in most cases this is a straightforward fix (clearing the drain line) rather than an expensive repair, but only if caught early.