A clogged AC condensate line is one of the most common reasons an air conditioner suddenly shuts off in summer, and you can usually clear it yourself in about 15 minutes with a wet/dry vacuum and a cup of vinegar. Here’s how to find the line, unclog it, and keep it clear.
What the condensate line does
As your air conditioner cools, it pulls moisture out of the air. That water drips off the indoor evaporator coil into a drain pan and flows out of your home through the condensate drain line, usually a 3/4-inch white PVC pipe. On a humid day, a typical central AC can remove many gallons of water.
Algae, mold, dust and sludge grow inside that dark, damp pipe. Over time they form a slimy plug, the water has nowhere to go, and the pan fills up.
Signs your condensate line is clogged
- The AC shuts off and won’t restart. Many systems have a float switch (also called a condensate overflow switch) that cuts power to the AC when water in the pan rises too high.
- Standing water in the drain pan or around the indoor unit.
- Water stains on the ceiling below an attic air handler.
- A musty or moldy smell near the indoor unit or from the vents.
- No water dripping from the outside end of the drain line on a hot, humid day while the AC is running.
What you’ll need
- A wet/dry shop vacuum
- Distilled white vinegar (about 1 cup)
- Duct tape or a rag
- A flashlight and towels
- Optional: a stiff brush or a short length of flexible tubing
How to unclog an AC condensate line
- Turn off the AC at the thermostat and switch off the breaker or the service switch next to the indoor unit.
- Find the drain line. Follow the PVC pipe that comes out of the indoor unit near the coil. It usually exits the house near the outdoor unit or runs to a floor drain, sump or condensate pump.
- Check the drain pan. If it’s full of water, soak or vacuum it out. If your unit has a removable secondary pan, empty it.
- Find the access port. Most lines have a T-shaped fitting with a removable cap or a short vertical pipe near the indoor unit. Remove the cap and look inside with a flashlight. You may see the clog right there.
- Vacuum the outside end. Go to where the line ends outdoors. Wrap the shop vac hose around the end of the pipe and seal the gap with duct tape or a rag. Run the vacuum for 1 to 2 minutes. You’ll often hear the clog break loose, and you’ll see sludge in the vacuum canister.
- Flush with vinegar. Pour about a cup of distilled white vinegar into the access port. Let it sit for 30 minutes, then flush with a little water to check that it drains freely.
- Restore power and test. Turn the breaker back on, set the thermostat to COOL, and after 15 to 30 minutes check that water is dripping from the outside end of the line.
If the AC still won’t start, the float switch may need a few minutes to reset after the water level drops. Some switches need to be reset manually.
How to prevent condensate line clogs
- Pour a cup of distilled white vinegar into the access port every 1 to 3 months during cooling season.
- Replace your air filter regularly. Less dust in the system means less sludge in the drain. See how often to change your air filter.
- Keep the outdoor end of the line clear of mulch, soil and plants.
- Ask your technician to check the drain and float switch during annual maintenance.
Avoid pouring bleach into the line regularly. It can be hard on PVC cement joints and some older metal drain pans, and many manufacturers recommend vinegar instead. Check your system’s manual if you’re unsure.
When to call a professional
Call an HVAC technician if:
- The vacuum and vinegar don’t clear the clog.
- The drain line is cracked, disconnected, or doesn’t slope downhill.
- The drain pan is rusted or cracked and leaking.
- Your system uses a condensate pump that isn’t running.
- Water has damaged ceilings, floors or insulation.
A drain line clearing typically costs $75 to $250, and replacing a condensate pump or float switch usually runs $150 to $400, depending on your area.
Frequently asked questions
Can a clogged condensate line stop the AC from cooling?
Yes. If your system has a float switch, it will shut off the AC to prevent a water overflow. Even without one, water backing up can lead to a frozen coil and water damage.
How often should I clean my AC drain line?
Flush it with vinegar every 1 to 3 months during the cooling season, and have it inspected at your annual tune-up.
Is it safe to use bleach in the AC drain line?
Occasional diluted bleach is used by some technicians, but vinegar is gentler and is the most common recommendation for regular cleaning. Never mix bleach and vinegar.
Where does the AC condensate line drain outside?
Usually near the outdoor condenser or foundation, as a short PVC pipe sticking out of the wall. In some homes it drains into a floor drain, a sump pit, a laundry standpipe or a condensate pump.
Still having cooling problems after clearing the drain? Work through our complete guide: AC Not Cooling? 12 Causes and How to Fix Each One.
Disclaimer: this guide is for general information only. Always turn off power before working near HVAC equipment. When in doubt, contact a licensed HVAC professional.