To prevent wear on the compressor.
It's a Lubricant. It lubricates parts.
to lubricate the compressor
mineral oil
The compressor oil
Oil in a AC compressor is there so that the mechanical parts don't over heat from friction
freon and oil
used as cooling and freezing agent
Ice
ACID
freon and oil
Package refrigeration equipment is a system that used for the process of refrigeration. Household refrigerators, industrial freezers, cryogenics, and air condition and big plants in industries for cooling purpose are the examples of package refrigeration equipment.
Sludge in refrigeration is a combination of water, acid and oil, normally this combination will eat the varnish on the windings of the compressor and short it out.