Air Conditioner Leaking Water Inside? Here’s Why
An air conditioner pulls moisture out of the air as it cools. That water is supposed to drip into a pan under the indoor coil and run away through a drain line or a small condensate pump. When water ends up on the floor around your furnace, in a ceiling, or running down the wall under a ductless head, something in that path is blocked, cracked or frozen. Most causes are cheap to fix if you catch them early. Left alone, they lead to water damage and mould.
Do this right away
- Turn the AC off at the thermostat so it stops making more water.
- Mop up the water and move anything that could get damaged, like boxes or rugs.
- Check the filter. If it’s clogged, replace it. A choked filter can freeze the coil, and the melting ice overflows the pan.
- Look for ice on the copper refrigerant line or the indoor coil. If you see ice, leave the system off and run the fan only for a few hours to thaw it.
Common causes
| Cause | Signs | Fix |
|---|---|---|
| Clogged condensate drain line | Water around the furnace, pan full, musty smell | Clear the line (vacuum or flush); add a cleaning tablet or treatment |
| Failed condensate pump | Small box near the furnace not running, water around it | Replace the pump; add a safety float switch |
| Frozen indoor coil | Ice on the line or coil, weak airflow, water after thawing | Fix airflow (filter, blower) or the refrigerant leak |
| Cracked or rusted drain pan | Steady drip under the coil even with a clear drain | Replace the pan or coil |
| Disconnected or poorly sloped drain line | Water at a joint, in the wall, or on the ceiling below | Re-secure and re-slope the line |
| Ductless head: blocked drain or wrong slope | Water dripping from the head or running down the wall | Clean the head and drain; correct the slope or add a mini pump |
| Condensation on ducts in a hot attic | Water spots on ceilings in summer | Insulate and seal the ducts |
What you can safely do
- Find the drain line, usually a white PVC pipe leaving the coil box, and check where it ends: a floor drain, a laundry standpipe, or outside.
- If there’s a cleanout cap near the coil, you can use a wet/dry vacuum at the outside end of the line to pull out the blockage.
- Listen for the condensate pump. If its reservoir is full and the pump doesn’t run, unplug it and call us.
When to call a technician
- Water keeps coming back after you’ve cleared the drain
- The coil or lines ice up. That usually means low refrigerant or an airflow problem.
- Water is in a ceiling or wall, or near electrical equipment
- The furnace in a combined system shows an error or shuts down. Many furnaces have a float switch that shuts everything off when the pan is full. See furnace leaking water.
Prevent it
Have the drain line flushed and the condensate pump tested at your yearly AC or heat pump service. Adding a safety float switch is inexpensive and shuts the system off before the pan overflows.
Water on the floor right now?
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