Refrigerant PT calculator

How it works

The calculator uses the same PT tables as the refrigerant pages. Each table runs in 1°F steps and was computed with CoolProp 8.0.0 (HEOS backend). Each one is compared with a published manufacturer chart or the NIST WebBook. The result of that check, including any blend where the published chart differs, is shown on each refrigerant page and on data sources. For example, the R-410A table gives 118.35 psig at 40°F dew, and the Chemours guide publishes 118.4 psig. Between rows the tool interpolates linearly.

The inputs:

• Refrigerant: the 62 on the site, grouped as on the refrigerant hub.
• Gauge pressure (psig) or temperature (°F). Typing in one box clears the other, so the tool always works in one direction.
• Elevation (optional, feet).

What you get:

• Single-component refrigerants (R-22, R-32, R-134a, R-290 and others) have one saturation temperature for each pressure.
• Blends show two values. The dew point (saturated vapor) is for suction pressure and superheat. The bubble point (saturated liquid) is for liquid line pressure and subcooling. This follows the Chemours and Honeywell charts.
• Temperature to pressure: the bubble and dew pressures (or the one saturation pressure). Below 0 psig the result is shown as inches of mercury vacuum.

Pressures are psig on a sea-level basis (14.696 psia), the same basis printed manufacturer charts use. Gauges read against local air pressure, so the elevation field converts between your reading and the chart. Enter a pressure and the tool converts your reading to the sea-level psig the chart uses. Enter a temperature and it shows what your gauge will read at that elevation.

Chart range: most refrigerants run from −40°F to 150°F. The low-pressure fluids R-11, R-123 and R-1233zd run from 0°F to 200°F. R-23 and R-508B start at −130°F, and R-717 covers −60°F to 130°F. R-744 (CO2) stops at 85°F because its critical point is about 87.8°F. Above that there is no saturation pressure to look up. Outside the range the tool tells you so.

Worked example

R-410A, 118 psig. The dew pressures are 116.09 psig at 39°F and 118.35 at 40°F, so the dew point is 39 + 1.91 ÷ 2.26 = 39.8°F. The bubble pressures are 116.52 and 118.79, so the bubble point is 39 + 1.48 ÷ 2.27 = 39.7°F. R-410A is a near-azeotrope, so the two values almost match.

R-448A, 40 psig. Dew 16.5°F, bubble 5.4°F. Honeywell’s own example gives “~16°F” dew at 40 psig. The 11°F gap between the columns is the glide. Reading the wrong one is the most common PT error on these blends.

R-123 at 40°F. The saturation pressure is −8.92 psig, so the tool shows 18.2 in Hg vacuum (8.92 × 2.036). That is normal for a low-pressure refrigerant at evaporator temperatures.

R-410A at 40°F dew, 5,000 ft. The chart says 118.35 psig at sea level. Local air pressure at 5,000 ft is about 12.23 psia instead of 14.70, so the gauge reads 118.35 + 14.70 − 12.23 = 120.8 psig for the same saturation temperature.

Reading the result

The PT value is a saturation temperature: the boiling or condensing temperature at that pressure. It equals the line temperature only where liquid and vapor are both present, inside the evaporator or condenser. The difference from the actual line temperature is superheat (suction) or subcooling (liquid). Use the superheat and subcooling calculators to get them directly.

For blends with glide, Tomczyk (ACHR News) puts the average evaporator temperature at the midpoint of the glide. Use the temperature glide calculator to see bubble, dew and midpoint together.

If the pressure is outside the chart for the refrigerant you picked, check that you picked the right refrigerant and that the gauge reads in psig.

Common mistakes

• One column for a blend. Older single-column charts switch columns at a cut-off. The Chemours guide shows saturated vapor at 50°F and below and saturated liquid at 52°F and above. Reading such a chart at the wrong end gives the wrong saturation temperature.
• psig vs psia. The tool works in gauge pressure. Convert absolute readings with the pressure converter.
• Ignoring elevation at mountain jobs. The error grows with altitude.

How to read a PT chart covers these step by step.