How to Seal a Leak in an Air Conditioner Line

Air conditioning lines found at the unit itself consist of copper.

Unlike ductwork, you cannot simply patch copper with water-mastic sealant and duct tape or aluminum tape. Instead, you must seal it to prevent it from leaking. If the leak is small, you can generally fix it with a few basic tools. However, large leaks may require you to replace the entire copper line.

Turn off the air conditioner and let the unit cool to room temperature. Dry the leaking line with a cloth or rag, removing any moisture that may be present.

Spread plumber's epoxy putty over the break or hole in the air conditioning line with a brush. Apply liberally and allow to dry as long as recommended by the manufacturer.

Wrap steel strapping around the plugged leak, cutting off excess with aluminum snips. Wrap tightly two to three times to seal the leak on the air conditioning line.

Place two bolt clamps over each end of the steel strapping and tighten down with a screwdriver or screw gun. Do not tighten too much or you may flatten or choke the air conditioning line.

Turn the air conditioner back on and monitor the patch for leaks. If moisture drips from one of the ends, remove the bolt clamps and steel strapping. Apply more epoxy putty, wrap the steel strapping around the line and fasten the bolt clamps.

Things You Will Need

  • Cloth or rag
  • Plumber's epoxy putty
  • Brush
  • Steel strapping
  • Aluminum snips
  • Bolt clamps
  • Screwdriver or screw gun


  • Alternatively, you can melt flux onto the leak with a propane or acetylene torch. When the flux dries, it will seal the line leak.
  • If efforts fail to stop the leak, the air conditioner line's integrity has been compromised. Replace the entire line if this is the case.

About the Author

Owen Richason grew up working in his family's small contracting business. He later became an outplacement consultant, then a retail business consultant. Richason is a former personal finance and business writer for "Tampa Bay Business and Financier." He now writes for various publications, websites and blogs.