NATE Air Conditioning and Heat Pumps Practice Exam 2025 – All-in-One Guide to Master Your Certification!

A crankcase heater is most needed when the compressor is off. The primary function of a crankcase heater is to prevent refrigerant from condensing in the compressor crankcase, which can occur when the system is not operating for an extended period, especially in colder environments. When the compressor is off, particularly in low-temperature conditions, the refrigerant can migrate back to the compressor and accumulate, leading to possible oil dilution or flooding. The crankcase heater maintains the temperature of the refrigerant and oil within the compressor, ensuring that the compressor operates smoothly upon starting and helping to avoid damage due to liquid refrigerant entering the compressor.

While there are other conditions where maintaining compressor function is important, such as during cooling cycles or in varying weather conditions, the specific need for the crankcase heater arises when the compressor is not in operation. This prevents issues during the next startup, making it crucial for overall system reliability and longevity.