How to clean a clogged air drain main drain pipe

A blocked main drain line from an AC will not only make your AC run out, it can also cause costly and expensive water damage in your home. This happens because the drain line takes the excess water from the evaporation unit of your AC, located inside your house, and drains it out. A main drain line of your plugged or clogged AC will quickly cause the drain pan under your evaporator to flood.


  1. Cut the electricity from the air conditioner so you can work on it safely. You can do this in a number of ways. One way is by locating the main switch and cutting off the power from there. In other installations, the AC unit may be installed in a sub-switch located on the outside (the condenser) of the unit. Finally, if you reach a part of the air conditioning unit, for example, if it is installed in a hallway, you can cut off the power supply of the unit itself.
  2. Look for the main drain line of the AC. These are normally made of PVC and will be placed outside your home. Look for the outlet of the drain line and clean any obstructions, such as leaves or mud, which may be blocking the end.
  3. Locates the entrance of the primary drainage line. These are connected to the drain pan under the evaporator part of the unit. The common places of installation of these are in the attics, basements or a hallway. The entry on the primary AC line will be larger than the secondary drain line, if present.
  4. Remove all water in the drain pan, if present. Small puddles can be cleaned with a towel or rags. Large puddles of water can be vacuumed with a vacuum cleaner or similar device. Cleaning the water will allow you to more easily locate the obstruction of the AC primary drain pipes.
  5. Use the brush to remove any mold or moisture from the opening of the main line. Insert the plastic tube along the main drain line. Continue inserting the pipe into the line until it is jammed. Remove the obstruction by moving the tube back and forth through the drain until the obstruction is undone.
  6. Mix a solution of one-quarter cup of chlorine in one gallon (3.79 l) of warm water. Pour into drain line carefully. Let the solution sit for at least fifteen minutes, then rinse by pouring cold water. When the line is open successfully, you should see the chlorine solution come out of the end of the drain line.
  7. Reset the AC drive current.

Tips & Warnings

  • Use a protective mask when working near mold, especially if you are sensitive to its spores.

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