How does the chart convert pressure to temperature?

Each refrigerant has a saturation curve fitted with Antoine-style coefficients that relate absolute pressure to saturation temperature. The tool adds standard atmospheric pressure (14.696 psi) to your gauge reading to get absolute pressure, then solves the curve for the matching temperature.

What is the difference between bubble and dew point?

Zeotropic blends like R-410A, R-404A, R-407C, and R-454B boil over a temperature range called glide. The bubble point is where liquid just starts to boil (used for subcooling on the liquid line); the dew point is where the last vapor condenses (used for superheat on the suction line). Near-azeotropic blends have small glide; R-22, R-32, and R-134a are single-component or azeotropic with no glide.

Which value do I use for superheat and subcooling?

Use the dew-point saturation temperature with the suction (low-side) pressure for evaporator superheat, and the bubble-point saturation temperature with the liquid-line (high-side) pressure for condenser subcooling. Mixing them up on a glide refrigerant skews your charge.

Is psig the same as the gauge reads?

Yes, manifold gauges read in psig (pounds per square inch gauge), which is pressure above atmospheric. The tool adds 14.696 psi to convert to psia (absolute) before solving the saturation curve. At sea level a gauge reading of 0 psig equals 14.696 psia.

How accurate is this chart?

The fitted curves match published refrigerant tables within about 1 to 2 degrees Fahrenheit across the normal HVACR operating range. For critical charging or laboratory work, verify against the manufacturer's official PT chart, but for field service this accuracy is well within practical tolerance.

What is the Refrigerant Pressure-Temperature (PT) Chart?

Interactive refrigerant pressure-temperature chart that converts gauge pressure in psig to saturation temperature for common HVACR refrigerants including R-22, R-410A, R-32, R-134a, R-404A, R-407C and R-454B, with bubble and dew points for blends. Runs in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Refrigerant Pressure-Temperature (PT) Chart

Name: Refrigerant Pressure-Temperature (PT) Chart
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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The refrigerant pressure-temperature chart converts a manifold gauge reading into the saturation temperature for the refrigerant in the system. It is the everyday tool behind superheat and subcooling, charge verification, and leak diagnosis, covering legacy and modern low-GWP refrigerants in one place.

How it works

For a pure or azeotropic refrigerant, saturation temperature is a single-valued function of pressure. The tool fits each refrigerant’s saturation curve and converts your gauge reading:

absolute pressure (psia) = gauge pressure (psig) + 14.696
saturation temperature   = curve(psia)   for the selected refrigerant

For zeotropic blends the chart reports two temperatures because the refrigerant boils over a glide: the bubble point (first bubble of vapor, used with the liquid line for subcooling) and the dew point (last drop of liquid, used with the suction line for superheat).

Tips and notes

Always pair the correct saturation value with the correct pressure: dew point with suction pressure for superheat, bubble point with liquid-line pressure for subcooling. R-410A, R-404A, R-407C, and R-454B have glide, so using the wrong end of the range can throw a charge off by several degrees. R-22, R-32, and R-134a behave as single temperatures. The fitted curves track published tables within a degree or two across normal operating pressures, which is fine for field service.

Refrigerant phase-out context

Understanding which refrigerants are transitional or legacy matters for service decisions:

Refrigerant	Status	Replacement
R-22	Phased out (production ended 2020 in the US)	R-407C, R-32, R-454B in new systems
R-410A	Being phased down (high GWP = 2088)	R-32 (GWP 675), R-454B (GWP 466)
R-404A	Phased down (GWP 3922, highest common HFC)	R-448A, R-449A in commercial refrigeration
R-407C	Lower GWP than R-404A; still in use	Variable by jurisdiction
R-134a	Phased down in mobile AC, still in chillers	R-1234yf in automotive
R-32	Lower GWP, growing use in split systems	Current-generation choice
R-454B	Ultra-low GWP blend; new residential systems	Emerging standard in US residential AC

Knowing the refrigerant type is the starting point for any PT chart reading — carrying a chart for the wrong refrigerant is a common source of incorrect charge decisions.

Practical superheat and subcooling workflow

For a standard split-system air conditioner:

Identify the refrigerant (data plate on outdoor unit).
Attach manifold gauges; read suction (low-side) pressure and liquid-line (high-side) pressure.
Use this tool to convert suction pressure → dew-point saturation temperature (for blends) or saturation temperature (for pure refrigerants).
Measure actual suction-line temperature with a clamp thermometer.
Suction superheat = actual temperature − saturation temperature at suction pressure.
Use this tool to convert liquid-line pressure → bubble-point saturation temperature.
Measure actual liquid-line temperature.
Subcooling = saturation temperature at liquid pressure − actual liquid temperature.

Typical targets vary by system and manufacturer, but a starting point for checking: 10–15°F superheat at the evaporator outlet and 10–20°F subcooling at the liquid line. Always consult the equipment manufacturer’s charging specifications.