How to Clean an Air Conditioner Overflow Pipe

Central air conditioning units keep homes cool during the hot summer months, but problems can occur if you don't care for your system properly. The overflow pipe in a unit is usually inside your air handler. It acts as a back up to the regular drainpipe allowing extra water to drain through it from the condensation caused by cooling the air. Mold and algae can also grow in the overflow pipe, however. Cleaning it once a year with bleach prevents the growth from clogging the pipe all the way.

  1. Turn off your air conditioner and access your air handler unit. The air handler is inside your home, probably in the attic or with your furnace, if you have central heat.

  2. Open the air handler's access door with the wrench or screwdriver. Locate the overflow pipe. It will be a pipe that drains into a pan under the evaporator on the inside of the air handler. The evaporator looks like a prism.

  3. Open a window in the room with the air handler. Place a funnel in the access hole of the overflow pipe. Plug the other end of the pipe. Pour 1 cup of bleach into the access hole slowly. Allow the bleach to sit in the pipe for two to five minutes.

  4. Unplug the bottom of the pipe and allow the bleach to flow into the drain pan. Rinse the pipe with clean water. Dispose of the bleach in the drain pan.

  5. Close the access door and turn the air conditioner back on.


  • Be sure the air handler room is well ventilated before you pour the bleach.

About the Author

Hollan Johnson is a freelance writer and contributing editor for many online publications. She has been writing professionally since 2008 and her interests are travel, gardening, sewing and Mac computers. Prior to freelance writing, Johnson taught English in Japan. She has a Bachelor of Arts in linguistics from the University of Las Vegas, Nevada.