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Air Conditioner Repair: Replace Rotted Insulation

Updated: Oct. 31, 2019

Replace rotting insulation on outside A/C lines

FH10OCT_ROTACI_01-2Family Handyman
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.

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Measure the A/C line diameter and order the insulation

Seal each end of the tubing

Wipe off the condensation and wrap a few winds of the sticky poly tape on the tubing where it exits the house. Then dry and wrap the service valve on the condenser end of the tubing. Squeeze it in tight around the tubing.

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 air conditioner 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

Install the new air conditioner foam

Slip the new air conditioner foam over the tubing and on top of the cork tape. Remove the adhesive liner, align the edges and press the seam together as you go. Be careful. Once the glued ends touch, you can’t get them apart again.

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.

  • Foam insulation