I have to test a Compressor that takes a 250vac 12uf Motor Run Cap. I have 12uf worth of those green 1000vdc Russian PIO caps could those stand in for a Motor Run?
Possibly, but they might not last too long. Caps intended for continuous AC use may be used for DC with no problem, but not necessarily the other way round. What will happen if one of the caps develops an internal short?