NATE Low Global Warming Potential (GWP) Practice Test

Glide is the varying saturation temperature that occurs during phase change for a zeotropic refrigerant blend. Because the blend contains components with different boiling points, the liquid-to-vapor transition doesn’t happen at a single fixed temperature. Instead, as the refrigerant boils in the evaporator or condenses in the condenser, the composition of liquid and vapor shifts and the temperature at which phase change occurs sweeps along a glide band.

This matters for charging and performance. When charging, technicians typically target specific superheat at the evaporator and subcooling at the condenser based on a fixed saturation temperature. With glide, that fixed point doesn’t exist, so using pure-refrigerant targets can lead to under- or overcharging, which hurts capacity and efficiency. You must account for glide by using the blend’s published glide data and adjust charging targets accordingly, ensuring you consider the changing evaporation/condensation temperatures across the evaporator and condenser.

In terms of performance, glide changes the effective temperatures at which heat is absorbed and released, influencing heat transfer rates, system capacity, and efficiency. Blends with negligible glide (azeotropic) behave more like a single-component refrigerant, while those with noticeable glide require special attention to charging and operating targets.