The difference in weight is so noticeable you can tell right away if it's copper or aluminum windings.
For those unable to detect the weight difference , every compressor has a date code stamped into the case learn how to decipher it, the early units all had copper. When did the manufactures start using aluminum.
Next you could start weighing some compressors, make chart up for reference.
Off Topic,,, Awhile back another member had a lead on a hot deal, copper wire still on the rolls with out a clue to figure the value. With a cheap OHM pocket type meter you can easily figure out how many feet of wire are left on the roll. There are other charts available that give the pounds per feet.
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