A compressor does not restart under the same conditions
After a brief interruption, pressure difference remains between suction and discharge sides. The motor must start against a higher mechanical load, which explains why immediate restart can produce unusually high current or stalled rotation.
Pressure equalisation is time-dependent
The required time depends on refrigerant circuit design, capillary dimensions, ambient temperature and compressor type. Three minutes is a practical convention, not a physical constant.
Low voltage makes restart more difficult
Starting torque falls when applied voltage is low, while current can remain high if the rotor fails to accelerate. Restart should require both elapsed time and acceptable supply voltage.
Repeated interruptions create cumulative stress
Repeated short cycling heats the motor winding, stresses the start device and erodes relay contacts. Protection logic should restart the timer after each new interruption.
Relay behaviour matters during restart
Relay contacts must close reliably under compressor inrush without excessive bounce or welding. Endurance testing should use a representative motor load rather than only a resistor.
The delay should be visible
A countdown or clear delay indicator prevents users from assuming the protector has failed and bypassing it.
Conclusion
The three-minute delay is an anti-short-cycle strategy. Its value comes from integration with voltage qualification, suitable relay capacity and appliance-specific restart logic.
References and scope
This article is an engineering interpretation for product selection and discussion. It does not replace applicable standards, electrical codes or appliance-manufacturer instructions.