One of the more common questions we get is how to wire potential relays in a refrigeration system. The reason we need potential relays as a star component is that start capacitors are not built for continuous duty. So we need a way to automatically drop the start capacitor out of the circuit. 

So as the compressor starts up and gets to about 75% of its speed a voltage is produced in the start winding then it opens up the relay to drop out the start capacitor.

So with that we can have a system that may have high staring torque or refrigerant that does not equalize and we need the boost right at beginning in order for the compressor to actually start.  Attached is a wiring diagram that should help you along the way.

Also attached is a more in depth look at potential relay operation.