Short answer
Turn the AC off at the thermostat and soak up the water. The usual cause is a clogged condensate drain line. Find where the small pipe ends outside and pull the clog out with a wet/dry vac for a minute or two. Then pour a cup of water into the access port near the indoor unit and check that it runs out outside. If it still leaks, call a technician.
Safety first
Turn the AC off at the thermostat before you work near the indoor unit, and do not touch outlets, cords or the unit while you stand in water. Never mix bleach with vinegar or other cleaners in the drain line: mixing chemicals can release toxic gas.
How to stop an AC leaking water inside
1Water around the indoor unit
The AC pulls moisture out of the air and drains it through a small pipe. When that pipe clogs, the water backs up and spills.
Read all the steps
- Water around the indoor unit. The AC pulls moisture out of the air and drains it through a small pipe. When that pipe clogs, the water backs up and spills.
- Turn it off and soak up the water. Set the thermostat to "Off". Lay towels down or use a wet/dry vac on the puddle, and move anything that can get wet.
- Look in the drain line access port. Near the indoor unit, the drain pipe usually has a T with a cap. Take the cap off. Water standing near the top means a clog.
- Pull the clog out from outside. Find where the pipe ends outside. Hold the hose of a wet/dry vac tight over the end, sealing it with a rag or tape, and run it one or two minutes.
- Pour water in, then back on. Pour a cup of water into the access port. If it runs out outside, put the cap back and set the thermostat to "Cool".
- Still not fixed? Call an HVAC contractor Especially if: water keeps coming back after you clear the drain line.
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Why it happens
- A clogged condensate drain line: algae, dust and slime build up inside the pipe. This is the most common cause.
- A float switch that shut the system off. It is a safety switch on the drain line or the pan that stops the AC when water backs up.
- A cracked or rusted drain pan under the coil.
- A frozen coil: when the ice melts, the extra water can overflow the pan.
- A broken condensate pump, if your unit pumps the water out instead of draining it downhill.
What not to do
- Do not mix bleach, vinegar or drain cleaners in the line. Mixing chemicals can release toxic gas.
- Do not force a wire or a snake into the pipe. You can crack the fittings.
- Do not bypass or remove the float switch to keep the AC running. It is what stops a flood.
- Do not ignore a wet ceiling under an attic unit. Turn the AC off and call.
When to call an HVAC technician
- Water keeps coming back after you clear the drain line.
- The indoor unit is in the attic and water is staining the ceiling.
- The drain pan is cracked or rusted through.
- The AC will not start again after the line drains.
Frequently asked questions
Why is my AC leaking water inside the house?
Most often the condensate drain line is clogged and the water backs up out of the pan. A frozen coil, a cracked pan or a failed condensate pump can also cause it.
How do I unclog my AC drain line?
Turn the AC off, find where the drain pipe ends outside and pull the clog out with a wet/dry vac for one or two minutes. Then pour a cup of water into the access port to make sure it drains.
Can I pour vinegar in my AC drain line?
Many technicians suggest a cup of white vinegar in the access port every few months to slow algae. Check your owner manual first, and never mix vinegar with bleach or other cleaners.
What is an AC float switch?
A small safety switch on the drain line or in the pan. When water backs up, it shuts the AC off to prevent a flood. Clearing the drain usually lets the AC start again.
Is it safe to run my AC if it is leaking water?
Not for long. Turn it off until you clear the drain. The water can damage ceilings, floors and the unit, and it can reach electrical parts.
Why did my AC stop working after the water backed up?
The float switch likely shut it off on purpose. Clear the drain line and let the water drain, and the AC should start again. If it does not, call a technician.