Amana upright frost free freezer, early 1970's...

Question

Freezer case has line voltage  (120 volts) in the case (box) .  The ground plug has been isolated with a 2 prong connecter.  Freezer runs in this  mode, other wise there is a "dead short to ground".  Is is likely the defrost heaters are shorted to case? or compressor has internal short?  My last test showed no short to ground (case) when compressor running but 120 volts in case when compressor off, pressumably when in drefrost cycle. The defrost timer was removed from contact with the case.  However previous test with every thing in place had 120 volts in the case when compressor was running and none  when compressor off----HUH?