When does the crankcase heater operate in the given schematic?

The crankcase heater is designed to prevent the compressor oil from flooding, which can occur when the compressor is off and refrigerant migrates to the crankcase. Typically, the crankcase heater operates when the compressor is off to maintain the temperature of the oil, ensuring it remains fluid and ready for operation when the compressor starts again.

In many systems, the heating element is energized during the off cycle of the compressor, making the scenario where it operates only when the fan is running incorrect. The fan operation does not necessarily correlate with the crankcase heater's function, as the heater's primary role is to maintain proper oil temperature in the absence of compressor activity, particularly when the unit is not running.

Understanding these operational conditions is crucial in maintaining system efficiency and preventing potential damage to the compressor, thereby extending its lifespan.