NATE Air Conditioning and Heat Pumps Practice Exam

Why is superheat necessary in a system that utilizes hermetic compressors?

1. It ensures that dry vapor reaches the compressor so that mechanical damage does not occur

2. It increases system capacity

3. It prevents liquid refrigerant from gassing the metering device

4. Superheat is necessary only when open compressors are being used

The correct answer is: It ensures that dry vapor reaches the compressor so that mechanical damage does not occur

Superheat is essential in a system utilizing hermetic compressors because it ensures that only dry vapor reaches the compressor. This is critical because the presence of liquid refrigerant can cause mechanical damage to the compressor. Hermetic compressors are sealed units that are not designed to handle liquid refrigerant; they function optimally on vapor. If liquid enters the compressor, it can result in hydraulic lock or other forms of damage, leading to system failure. Superheating the refrigerant in the evaporator allows it to transition fully to vapor before it reaches the compressor, thus protecting the compressor from potential damage and ensuring reliable operation. The other options highlight different aspects of refrigerant behavior but do not directly address the core need for superheat in protecting hermetic compressors. For instance, increasing system capacity and preventing liquid refrigerant from reaching the metering device are important but not the primary reasons for superheat in this context. Lastly, stating that superheat is only necessary for open compressors overlooks the critical protective function it serves in hermetic compressors specifically.