David- from your description it sounds like the voltage is far lower than the motors are expecting.

Check the voltage at the motors when they are running. I suspect that 120 volt motors are only getting 100 or so. 240 volt motors perhaps 200. That causes an increase in current and burns up the motors and switches like you described.

Compressors draw LOTS of current. When the motors are not running everything will appear normal.

Let us know what you learn with the voltmeter..

D