I have noticed the refrigerant pipe that is inside the condenser, the one that connects to the compressor, was sweating the other day. I did read on here as far as energy efficiency goes it does not need to be insulated. enter image description here But please see the attached image, the pipe is turning green. Is that corrosion? Should I just insulate that small section? putting the insulation right up against the connector junction?

  • 4
    Copper patina It will turn green but it’s not corroding. I would leave it as is.
    – Kris
    Aug 30, 2021 at 2:28
  • 4
    technically it is corroding, but that's certainly not a problem,
    – dandavis
    Aug 30, 2021 at 3:35
  • "Is that corrosion?", "Should I insulate?", and "What kind of insulation?" are really 3 different questions you're asking here. It seems that, so long as the condensate has somewhere safe to go (i.e. it's not going to drip onto wood & rot through something), there's nothing to worry about, but you may want to consider editing your post to focus on only one question.
    – FreeMan
    Aug 30, 2021 at 13:04

1 Answer 1


The corrosion/patina on the copper might seem like a bad thing because you're used to rust on steel, but it's not the same process. Rust on steel doesn't form a good bond on the metal, it expands, and it flakes off, exposing more steel that then rusts and flakes off, etc. It's a destructive process.

Copper an aluminum corrode much, much slower because the compounds they produce are bound tightly to the surface of the metal and actually create a protective coating that prevents further corrosion. Aluminum loves to bond with oxygen, so bare aluminum rapidly oxidizes (corrodes, "rusts"), but that forms a hard layer of aluminum oxide that keeps more oxygen out. The process is similar with copper, but with different compounds.

Those AC components are produced like that with full knowledge that it will have rain and condensation on it all the time. The patina won't be an issue and doesn't need anything to stop it.

  • wow! thank you so much, this is the most informative answer. you explained the reason of the appearance, the difference in corrosions, and the reason to leave it be. the answer is concise and informative. 👍🏻
    – 6zz
    Aug 30, 2021 at 16:24

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