I have an old 1980s subzero refrigerator that is powering up but no longer cooling effectively. It appears at some point the compressors were replaced with r134a.
There is a black char/blob/residue on the refrigerant lines going into and out of the freezer evaporator on the top of the unit. It feels reasonably hard to the touch and did not stick when I poked it.
Is this residue from compressor oil leaking and is indicative of a leak, or is it just burnt insulation? Or something else?
