What do potential relay contacts open in response to?

The correct answer is based on the function of potential relays in air conditioning systems. Potential relays are designed to monitor the counter electromotive force (EMF) generated by the motor during its operation. When the current flows through the start windings of a compressor motor, it generates a voltage that opposes the applied voltage, which is the counter EMF.

As the motor reaches its normal operating speed, the counter EMF increases. Once this EMF surpasses a certain threshold, it signals the potential relay to open its contacts, thereby disconnecting the start windings from the circuit. This action is crucial because it allows the motor to run efficiently using only the run windings, preventing potential overheating and damage that could occur if the start windings remained energized.

This function of opening contacts in response to the increase of counter EMF ensures that the motor operates optimally and efficiently, maintaining the necessary balance for effective cooling in residential air conditioning systems.