Refrigerant PT Chart

A pressure–temperature chart gives you the saturation temperature of a refrigerant at a given pressure — the temperature at which it boils or condenses at that pressure. That single number is the reference point every charging calculation is built on.

In a running system the refrigerant is only at saturation inside the evaporator and condenser. Everywhere else it's either subcooled liquid or superheated vapor, and the difference between the saturation temperature and the actual line temperature is exactly what you're measuring when you check superheat or subcooling.

• Superheat = measured suction line temperature − saturation temperature at your suction pressure. Take the suction pressure, find its saturation temperature here, then subtract.
• Subcooling = saturation temperature at your liquid pressure − measured liquid line temperature. Find the saturation temperature for the liquid pressure, then subtract the measured liquid line temperature.
• The targets come from the manufacturer's charging chart or the unit nameplate — the PT chart only supplies the saturation reference.

Worked example: R-410A at 118 psig saturates near 40°F. If the suction line measures 52°F, superheat is 12°F.

Blends behave differently from single-component refrigerants: because they're mixtures, they glide — the saturation temperature shifts as the blend boils or condenses. Use the dew point for superheat and the bubble point for subcooling.

The values here are interpolated reference points, good for field math and sanity checks. For charging, always use the manufacturer's published PT chart for the exact refrigerant blend in the system, and follow the equipment's charging chart — especially on blends and A2L refrigerants, where glide and safety handling both matter.