Blended Refrigerants: Temperature Glide, Bubble/Dew Points, and P-T Chart

Single-component refrigerants have a fixed boiling point. Heating a subcooled liquid to its boiling point shows a flat region where liquid changes to vapor; until all liquid is vapor, then the vapor can be superheated.
Blended refrigerants have no fixed boiling point. They exhibit temperature glide: boiling begins at the component with the lowest boiling point and occurs over a range of temperatures, not at a single point.
Glide range can vary widely depending on the blend: from as little as $2^\circ F$ up to $14^\circ F$ (or more in some blends).
Key terms: bubble point (start of boiling for subcooled liquid) and dew point (temperature at which vapor would begin to condense back to liquid).
Bubble point and dew point define the boiling/condensing range for blends, unlike a single-component refrigerant which has a fixed boiling point.

Bubble point: the temperature where subcooled liquid first begins to boil; used for subcooling measurements.
Dew point: the temperature where vapor would begin to turn into liquid when cooling; used for superheat measurements.
For blended refrigerants, dew point and bubble point correspond to different ends of the boiling range.
Dew point is associated with lower temperatures (low-side measurements); bubble point with higher temperatures (high-side measurements).

The chart shows saturation pressures for a given temperature; the x-axis lists refrigerants, the y-axis shows temperature.
On the chart, dew point numbers appear in the lower-temperature region (low side); bubble point numbers appear in the higher-temperature region (high side).
When checking superheat, read the dew point numbers in the lower temperature range.
When checking subcooling, read the bubble point numbers in the higher temperature range.
This chart helps interpret how blends behave across the subcooling and superheat ranges, due to their temperature glide.