When should the crankcase oil heater be ON?

The crankcase oil heater should be on when the compressor is off to ensure that the oil remains warm and prevents it from flooding the compressor with excess liquid refrigerant during periods of rest. When a compressor is not operating, refrigerant can migrate into the crankcase and mix with the oil, making it difficult for the compressor to start and leading to potential damage.

By heating the crankcase oil, the heater helps keep the oil at a sufficient temperature to maintain proper viscosity and prevent the formation of sludge, which can hinder the compressor's performance. This practice is especially important in low-temperature environments where the likelihood of refrigerant migration into the oil is increased.

The other scenarios do not prioritize the oil's temperature management as effectively and could risk operational issues when the compressor starts back up if the oil is not properly conditioned.