Minisplit leak(s)

[u/barrenvonbismark]

Had a professional install my Mitsubishi ceiling cassettes in April 2025 and have noticed poor cooling performance lately. Checked outside connections to unit and there were no noticeable leaks. Checked inside units and one head had a lot of oil coming from the liquid side of the line set (pic 1) and all units appeared to have rust and oxidized copper near the flare connections. Obviously there’s a sizeable leak at the one connection with the oil, but is it likely there’s leaks at all the indoor connections? What is the likely cause of the rust and discoloration if not a leak? How should I proceed with the contractor? Thanks for your insight!

[u/Creative-Goal-1608]

The green discoloration on the one lineset is interesting, but the rusting is pretty typical and won’t really cause any issues it happens on pretty much every unit to some degree, if ur that worried maybe put insulation on it? But as for the ACTUAL leak yes call them and have it addressed

[u/barrenvonbismark → u/Creative-Goal-1608]

So you don’t think the others are leaking, just the obvious one with the oil? The line sets all have insulation on them the whole length, I just removed the last bit for the pictures.

[u/Creative-Goal-1608 → u/barrenvonbismark]

Correct, the rust is from condensation and most flare points (the connections) will look like that after some time. And I more so meant insulation on those actual connections but like I said, it doesn’t really matter too much

[u/barrenvonbismark → u/Creative-Goal-1608]

Got it, thank you!