Refrigerant PT chart and saturation lookup

How the lookup works

The chart is a table of saturation pressure for every whole degree from -40 to 140°F, computed with CoolProp 8.0.0, an open thermophysical property library. Between whole degrees the calculator interpolates in a straight line. Going from pressure to temperature it runs the same table backwards. It never extrapolates past either end.

Pressure from temperature

P = P(T1) + (P(T2) - P(T1)) x (T - T1)T1 and T2 are the whole degrees either side of the temperature you enter. The table steps are small enough that the straight line adds less error than a gauge needle can show.

Temperature from pressure

T = T1 + (P - P(T1)) / (P(T2) - P(T1))The same table read the other way, so a round trip from temperature to pressure and back lands where it started.

Dew point and bubble point

P_bubble(T) > P_dew(T) on a blendA blend boils over a range of temperatures. The dew point line is where the last drop of liquid boils off, the bubble point line where the first bubble forms. R-22 and R-32 are single refrigerants and have one line.

Temperature glide

glide = T_dew(P) - T_bubble(P)At one pressure the dew point sits above the bubble point. On R-454B at a 107.5 psig evaporator that gap is 2.7°F. On R-410A it is a fraction of a degree.

Gauge reading at altitude

P_gauge = P_abs - p_atm, p_atm = 14.696 x (1 - 6.8754e-6 x Z)^5.2559A manifold reads pressure above the air around it. The standard atmosphere from ASHRAE Handbook Fundamentals, Chapter 1, gives p_atm in psia at elevation Z in feet. Printed charts assume 14.696 psia, which is sea level.

Readings you see on real systems

Each row runs through the same lookup the form uses. Blends show the dew point first and the bubble point second.

On R-454B at 40°F the bubble point line sits 5.7 psi above the dew point line. Read the other way, at the 107.5 psig dew pressure the liquid starts to boil at 37.3°F, 2.7°F below the dew point. That gap is why a blend has two columns and why the line you read matters. R-454B also runs 10.9 psi lower than R-410A at the same 40°F dew point, so an R-410A chart on an R-454B system gives the wrong answer.

In Denver, at 5,280 ft, the air around the gauge is at lower pressure, so every reading comes out 2.6 psi higher than at sea level. Look that R-410A reading up on a sea-level chart and the saturation temperature comes out 1.2°F too warm, which shows up directly as an error in superheat.

Saturation pressure chart, -20 to 130°F

Gauge pressure in psig at sea level. The R-410A column is the dew point line; its bubble point line runs at most 1.2 psi higher over this range. R-32 and R-22 have one line.

The chart is printed from the same tables the calculator reads, so the two cannot disagree.

Data sources and check charts

• CoolProp thermophysical property library, version 8.0.0 - saturation pressures for R-410A, R-454B, R-32 and R-22 (Bell, Wronski, Quoilin and Lemort, Industrial and Engineering Chemistry Research, 2014).
• Daikin Comfort Technologies, A1 vs. A2L Pressure Temperature Chart, USA - check points for all four refrigerants from -38 to 140°F, values supplied by Weitron.
• Honeywell, PT Chart Solstice 454B (R-454B) - check points for the R-454B dew and bubble lines from 20 to 500 psig.
• Chemours, Thermodynamic Properties of Opteon XL41 (R-454B), Engineering Units - check points for the R-454B liquid and vapor pressures, based on NIST REFPROP version 10.
• Honeywell, Genetron Refrigerants Pressure Temperature Chart - check points for R-22 and R-410A (AZ-20).
• Arkema, Forane Refrigerants Pressure Temperature Chart, High Elevation (5,000 ft.) - check of the altitude correction for R-22, R-32 and R-410A.
• ASHRAE Handbook Fundamentals, Chapter 1, standard atmosphere - atmospheric pressure at the elevation you enter.
• EPA Clean Air Act Section 608 - technician certification and refrigerant handling rules that apply whenever gauges go on a system.

Limits of this chart

• The table runs from -40 to 140°F saturation. Outside it the calculator refuses instead of guessing. Below 0 psig a gauge is in vacuum, and this chart has no entry for it.
• R-22, R-410A and R-32 values agree with the Daikin chart within 0.5 psi across the range, and R-22 and R-410A agree with the Honeywell Genetron chart within the same 0.5 psi.
• Published R-454B charts do not agree with each other. Honeywell and Chemours use different property models for the blend, and near condensing pressures their charts are about 2 psi apart. Our R-454B values are within 0.5 psi of the Daikin chart up to 100°F and within 1 psi up to 140°F. Against Honeywell and Chemours they are within 2.5 psi, except the Chemours bubble line at condensing temperatures, where the gap is up to 3.5 psi.
• When you charge a system, the chart and the installation instructions from the equipment manufacturer come first. This page looks up a reading and does not overrule them.
• The altitude correction uses the standard atmosphere. Weather moves the local barometer too, and a high or low pressure system shifts the gauge zero by a few tenths of a psi.
• The chart gives saturation only. A line temperature above or below saturation is superheat or subcooling, which the superheat and subcooling calculator works out from your readings.
• Non-condensables, a mixed or contaminated charge, or the wrong refrigerant in the system put the pressure off the chart for any temperature. A PT chart cannot tell you which of those you have.

Common PT chart mistakes

1. Reading superheat off the R-454B liquid column. At 107.5 psig the R-454B dew point is 40°F and the bubble point is 2.7°F lower. Superheat read off the bubble line comes out that much too high, and a tech charging by superheat adds refrigerant the system does not need.
2. An R-410A chart on an R-454B system. The two run at different pressures. An R-454B evaporator at a 40°F dew point reads 107.5 psig, which an R-410A chart calls 35.1°F. Check the data plate and set the digital manifold to the refrigerant that is actually in the system.
3. Forgetting the elevation. In Denver a gauge reads about 2.6 psi higher than at sea level for the same refrigerant. On an R-410A evaporator at 40°F, a sea-level chart puts that reading about 1.2°F too warm.
4. Mixing up psig and psia. Manifolds and field PT charts read psig. Engineering tables and some property software print psia, which is 14.7 psi higher at sea level. Mixing the two moves the saturation temperature by several degrees at evaporator pressures.
5. Reading saturation off a system that is not running. With the compressor off, the pressure settles toward the saturation pressure of the coolest place liquid is sitting. It tells you the refrigerant is there and roughly what it is, not how the system is charged.

Questions about PT charts

Related pages

• The A2L refrigerant transition Where R-454B and R-32 stand, and what changed for installers in 2026.
• Static pressure calculator Low airflow looks like low charge on the gauges. Check the duct side first.
• Dew point calculator Sweating on the suction line and the air handler.
• BTU to tons converter Capacity in BTU/h, tons, kW and MBH.
• All tools Every public BuildSolver calculator in one list.

Used on the same service call

• Superheat and subcooling calculator Turn the saturation temperature into a charge check with your line temperatures.
• HVAC CFM calculator Confirm airflow per ton before you touch the charge.
• Psychrometric calculator Indoor wet-bulb for a fixed-orifice superheat target.