I put the circuit on slightly bigger breakers and tried again. The result is that my phase converter (17.5 HP idler capacity) is not big enough to restart the compressor when PSI reaches 100. I do not suspect unloaders, based on what I hear when it starts, unloaders do work.
This time motor overloads tripped, quite rightly. I would not try to defeat them. The motor clearly was not doing well.i