AC Water Leaks: Causes and First Steps

Where the Water Comes From

Warm indoor air holds moisture. When it passes over a cold evaporator coil, that moisture condenses, drips into a pan and drains away. Over a humid day a residential system can produce several gallons. Everything about that process is normal — until the water leaves the intended path.

Common Causes

That last cause is worth noting because it does not involve the drain at all. In humid conditions, an uninsulated or poorly insulated suction line sweats, and the resulting drip can look exactly like a drain leak.

• A clogged condensate drain line, usually from algae and dust buildup
• A cracked, rusted or misaligned condensate pan
• A drain line with incorrect slope or a missing trap
• A frozen evaporator coil melting faster than the drain can handle
• A failed condensate pump on systems that require one
• A disconnected or improperly sealed drain fitting
• Poor insulation on refrigerant lines causing surface condensation

What to Do Immediately

Turn the system off at the thermostat. As long as it runs, it keeps making condensate and keeps feeding the leak. Place towels or a pan to contain water and protect flooring and ceilings.

Look for the source. Water in the secondary pan under an attic unit usually means the primary drain is blocked. Water dripping from an exterior wall outlet, often above a window, means the secondary drain is carrying water the primary should be handling. Standing water in the primary pan means the same thing.

If water has already reached a ceiling, address the moisture promptly. Drywall holds water and can fail without much warning.

Why the System Sometimes Shuts Itself Off

Most modern installations include a float switch that interrupts operation when water rises in the pan. If your system stopped working and you find standing water, the switch did its job. Clearing the blockage and resetting is the fix — but the blockage is the actual problem and should be cleared properly rather than bypassed.

Never bypass or disable a float switch to keep cooling running. That protection exists specifically to prevent ceiling and flooring damage.

Prevention

• Have the drain line flushed during annual maintenance
• Use condensate pan treatment tablets during the cooling season
• Keep filters fresh so less debris reaches the pan
• Confirm a secondary pan and float switch exist under attic equipment
• Watch for water at the exterior secondary drain outlet
• Have line-set insulation inspected and replaced when degraded