Since it is likely that your evaporator core in the old Frigiking was last used with R-12 (also known by the brand name Freon), R-12 compressors used a different oil than today’s R-134a compressors. Therefore, if it were mine, I would get the evaporator flushed out and dried with nitrogen. Flushing products can be acquired at the local auto parts store. There are also numerous YouTube videos that go through the process.