A/C Drain Line Clogged? How to Clean and Unclog It

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An AC drain line clog can quickly lead to the air conditioner shutting down or worse, leaking and causing major water damage to your home.

This post answers a couple questions with directions for how to clear a drain line clog plus links to useful videos.

Signs of a Clogged Drain Line or Pan

If you’re sure the drain pan or line is clogged, you might want to skip to Clear a Clogged Drain by Hand or Clear a Clogged Drain with Vacuum and Hose.

There are two common signs of a clogged drain line:

  1. The AC won’t start
  2. The drain pan leaks

The drain pan and drain line are in the bottom of the air handler. As the AC runs, moisture from the air condenses on the indoor coil, runs off the coil into the pan and down the drain.

Debris called sludge can build up in the drain line. It’s usually some combination of dust, dirt, mold, algae, hair and fur.

The AC won’t start: Many drain pans have a float. If the condensate doesn’t drain, the pan will fill up, raise the float and shut down the AC. It’s like the float on a dehumidifier.

If your air conditioner won’t turn on even though the thermostat is calling for AC, this could be the problem. Our AC Problems Troubleshooting Guide discusses the full range of potential problems to consider.

Leaks: If the area around the air handler or furnace is wet, shut down the system immediately. Not all pans have a float – or the float might fail.

How to Unclog a Drain Line or Drain Pan

There are two proven approaches to clearing the drain line. They explain how to unclog ac drain line in attic, basement, garage or wherever your air handler or furnace is located.

  • By Hand – Best for Clogged Pan
  • Using a Shop Vac & Hose – Best for Clogged Line

Pro Tip: We recommend using both methods to thoroughly clear the problem. The first addresses the pan. The second cleans the drain line that runs out of your home.

Clear a Clogged Drain Pan by Hand

The first step is to locate the drain pan. It’s beneath the indoor coil in the air handler, furnace or its own small cabinet attached to the air handler. As this picture shows, it might also be in the plenum.

drain pan

The pan is beneath the evaporator coil.

Now, follow these steps to clean a drain line and pan.

  1. Clean out the pan. If it is full of water, use a towel or a shop vacuum with the paper filter removed to remove the water. Scrape out any sludge you find there.
  2. Locate the drain hole. Use a thin but stiff wire brush to clean the drain hole and as far as the brush reaches.

A useful set like this one(amazon link) includes a brush, auger, plastic snakes that are great for grabbing and removing clogs and a longer wire snake. You’ll find many uses for these tools around the house, not just unclogging the AC drain line. 

The tools can be used two other locations:

  • In the condensate line, accessed by the vent tee, as seen in the image showing the condensate tray
  • In the AC drain line on the outside of your home – near the AC condensing unit.

AC drain line on the outside of your home

  1. Sanitize the pan and drain. Mix 1 cup of bleach and a ½ cup of water. Pour the mixture into the pan to sanitize the pan and drain and help prevent future clogging.

For an ecofriendly approach, use 2 cups of white vinegar, undiluted, instead of the bleach mixture.

  1. Use pan tablets to prevent a re-occurrence. Place 3 or 4 condensate pan treatment tablets(amazon link). They’ll last about a month, and then you will need to add more.

Unclog AC Drain Line with Vacuum and Hose

This approach will clean out the drain line from the drain pan to the end of the drain outside your home.

Using just the shop vac might be enough. Consider or try both ways to see which works best for your system. The vacuum approach is better for how to unclog ac drain line in attic, since running a hose up there is difficult.

  1. Locate the end of the condensate drain outside.
  2. Fit the end of the vacuum over the condensate line, and use duct tape to create a secure, airtight connection. This can be difficult because the drain line is ¾” and your vacuum hose might be 2-4 inches depending on the model.

Instead of tape, this tool(amazon link) fits most shop vacs and has a 1-inch side to snugly fit the outer diameter of the condensate drain.

  1. Turn on the shop vacuum for about 3 minutes. Remember to remove the paper filter. If it gets wet, it will soon mold.

This method is shown in this video.

If you really enjoy DIY projects and want the best long-term solution to a clogged drain line, then take this next series of steps using PVC parts.

Approach this project with the AC turned Off.

  1. Cut the drain line. Add a shut-off valve at the air handler or furnace side. Turn it to the Off position.
  2. Add a T on the opposite side, and insert a garden hose fitting into the top of the T.
  3. Screw into the garden hose fitting a ¾” to ½” adapter, and screw into the adapter a short ½” threaded nipple. Add a cap to the threaded pipe. This will secure and close the line when you are not cleaning it.
  4. Dry-fit the pieces, and when you know its correct, use PVC glue to secure them together. Do not glue the nipple into the garden hose fitting.
  5. Double-check that the valve is Off. Remove the cap assembly – the threaded nipple and cap – from the garden hose fitting. Attach a garden hose, and turn it on for a few minutes. Turn off the hose and detach it.
  6. Pour bleach mixture or straight white vinegar into the line before replacing the cap.

Want a visual? This video demonstrates this method and offers a few extra techniques. We like the “optional but necessary” step!

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