My mini-split was installed sometime between fall 2017 or spring 2018 when my house was built. It failed when it was 6 years old, and the lineset had to be replaced because there was too much acid in the insulation and it corroded the copper.
The problem was that the lineset was in my walls, so replacing it would require ugly lineset in a highly-visible place on my house. All the quotes to fix / replace it were absurdly expensive.
Because the mini-split was for a room that I use occasionally, I just use a portable air conditioner and a space heater.
Quality control by the contractor is soooo important. Formicary corrosion like you described can happen if a contractor doesn't pull a proper vacuum on the system to evacuate moisture before releasing refrigerant. I saw an anecdote where Bill Spohn, who literally owns an HVAC tools company, had this happen with the contractor installing a system in his own house! (https://www.heatpumped.org/p/are-heat-pumps-a-commodity)
I suspect it's especially bad with new builds, as new builds are a race to the bottom and every subcontractor is fighting to get the lowest bid. The best way to make it cheaper is skip steps, and that hurts in the long run. Sorry you ended up in that situation, crummy experiences like this set the industry back. For what it's worth, the same corrosion could happen with a traditional AC system too (it's not just heat pumps). But the difference is, often those refrigerant lines don't get as hidden on interior walls as the ones for ductless mini-splits do.
> The white insulation material, typically made of polyethylene or similar compounds, was found to degrade prematurely when exposed to UV radiation.
According to my contractor, this was a problem with lineset manufactured in 2016 and a little after. All of the HVAC companies that I called understood the "white lineset" problem.
pretty sure the white insulation on the lineset, when exposed to moisture and UV, can create an acid that eats the copper. thats probably what happened
The problem was that the lineset was in my walls, so replacing it would require ugly lineset in a highly-visible place on my house. All the quotes to fix / replace it were absurdly expensive.
Because the mini-split was for a room that I use occasionally, I just use a portable air conditioner and a space heater.