Air Conditioner Repair: Replace Rotted Insulation

Replace rotting insulation on outside A/C lines

Rotting insulation on your outdoor A/C lines can cost you energy. The fix is simple. We show you how to do it and tell you where to get the special insulating foam.

By the DIY experts of The Family Handyman Magazine

Measure the A/C line diameter and order the insulation

Condensation that forms on your outdoor A/C lines reduces efficiency and raises your energy costs. So you need to install new insulation. Start by peeling off all the old foam insulation.. Then measure the outside diameter on the larger of the two tubes (the skinny tube doesn’t need insulation). Unfortunately, you won’t find the right insulation at any home center. Instead, contact a refrigeration supply house or online supplier for new foam and insulating tape (Insul-Lock tubing insulating foam, and Nomaco Poly Tape, both from

Cut the new insulation to length.

Measure the length of the A/C line and cut the insulation a few inches longer. Leave the adhesive liner in place and install the insulation.

Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

  • Tape measure
  • Utility knife

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.

  • Cork tape
  • Foam insulation

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