The start capacitor in a hard start kit applies extra torque to the start winding, but overheating is a problem if the start capacitor is allowed to remain in the circuit. That's why potential relays exist in hard start kits; they take start capacitors out of the circuit to prevent the windings from overheating. Ty Branaman came to Kalos and gave a great class on HVAC compressors, especially in the areas of capacitor wiring, hard start kits, and voltage drop. You can watch it at https://buff.ly/