What is a key characteristic of a medium-pressure appliance?

The defining feature of a medium-pressure appliance is that it operates with refrigerants having saturation pressures between 45 psia and 170 psia. This range distinguishes medium-pressure systems from low-pressure and high-pressure appliances, which operate at lower and higher saturation pressure levels, respectively. Understanding these pressure thresholds is critical for technicians, as they affect the design, safety, and handling of refrigeration systems.

The other options, while related to refrigeration systems, do not accurately define a medium-pressure appliance. For instance, the saturation pressure below 45 psia is characteristic of low-pressure appliances, while the notion of using a single refrigerant type is not exclusive to medium-pressure systems, as appliances of all pressure categories can utilize different refrigerants. Lastly, being hermetically sealed relates to the physical design of certain appliances rather than their pressure classification. Thus, the selection of the option focusing on saturation pressure is pivotal for correctly identifying medium-pressure appliances.