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Refrigerant PT Charts

Pressure temperature charts for 11 common refrigerants, each with a lookup, metric toggle, typical operating pressures and worked superheat and subcooling examples.

By BrazeJobs Team · Updated

What a PT Chart Tells You

A pressure temperature (PT) chart lists the saturation pressure of a refrigerant at each temperature. Where liquid and vapor exist together, as in an evaporator or condenser, pressure and temperature are locked together, so a gauge reading tells you the temperature the refrigerant is boiling or condensing at.

Techs use PT charts to work out superheat and subcooling, to check that a system has the refrigerant its nameplate says, and to check standing pressure on a system that has been off. Each refrigerant has its own curve, so using the wrong chart gives the wrong answer.

Every chart on this site comes from a published source, cited on its page, and was cross-checked against CoolProp, an open-source library of refrigerant properties.

Which Chart Do You Need?

Start with the nameplate on the outdoor unit or condensing unit, which lists the refrigerant and factory charge. After a retrofit, look for a tag or sticker naming the new refrigerant and oil, since the nameplate still shows the original.

Cylinder color is no longer a reliable guide. Under AHRI Guideline N, refrigerant cylinders moved to one light gray color by 2020, with a red band or top marking flammable refrigerants such as A2Ls and R-290. Read the label instead.

If the nameplate is missing, a standing pressure check narrows it down, as in the example below, and a refrigerant identifier confirms it before you recover or add anything.

Saturation Pressure by Refrigerant (psig)

Vapor (dew) pressure at four common temperatures. For blends, the liquid (bubble) pressure is higher; see each chart for both columns.

Values from the chart on each refrigerant’s page. "inHg vac" means vacuum. GWP: IPCC AR4.
RefrigerantSafetyGWP20°F40°F70°F100°F
R-22A11,81043.168.6121.4195.9
R-134aA11,43018.435.071.2124.0
R-410AA12,08878.4118.4201.1317.6
R-404AA13,92254.584.4147.0234.0
R-454BA2L46670.9107.7184.0291.6
R-407CA11,77438.063.1117.0196.0
R-32A2L67580.0121.0205.8325.7
R-290A3341.164.0110.2173.9
R-448AA11,38744.672.1130.0214.0
R-1234yfA2L421.638.473.9125.0
R-422BA12,52635.559.4110.0183.0

Bubble Point, Dew Point and Glide

Single-component refrigerants such as R-22, R-32, R-134a, R-290 and R-1234yf boil at one temperature for each pressure, so their charts have one column. Near-azeotropic blends such as R-410A behave almost the same way.

Zeotropic blends boil over a range. The bubble point is where liquid starts to boil, the dew point is where the last liquid is gone, and the difference is the glide. Use the dew column for superheat and the bubble column for subcooling.

Glide also means blends must be charged as liquid. Charging vapor from the cylinder pulls off more of the components that boil easily and changes the mix in the system.

  • R-410A: about 0.2°F of glide at a 40°F dew point.
  • R-454B: about 2.6°F of glide at a 40°F dew point.
  • R-407C: about 11.5°F of glide at a 40°F dew point.
  • R-448A: about 10.1°F of glide at a 40°F dew point.
  • R-422B: about 7.3°F of glide at a 40°F dew point.

Superheat and Subcooling Formulas

Convert the gauge pressure to a saturation temperature with the chart, then compare it with the line temperature.

Superheat

SH = Tsuction − Tdew

Subcooling

SC = Tbubble − Tliquid

Vacuum

inHg = −psig × 2.036

Tsuction
Suction line temperature, °F
Tliquid
Liquid line temperature, °F
Tdew
Dew point at suction pressure, °F (saturation temperature for single components)
Tbubble
Bubble point at liquid pressure, °F (saturation temperature for single components)

The superheat calculator does these lookups for all 11 refrigerants.

Worked Example: Identify a Refrigerant by Standing Pressure

A split AC with a missing nameplate has been off all morning. Indoor and outdoor temperatures are both about 76°F, and the gauges read 211.9 psig on both sides.

  1. R-22 at 76°F: 134.5 psig.
  2. R-410A at 76°F: 222.2 psig.
  3. R-454B at 76°F: 211.9 psig.
  4. R-32 at 76°F: 226.7 psig.

Result: the reading matches R-454B. Confirm with a refrigerant identifier before recovering or adding refrigerant, since a mixed or contaminated charge can read anywhere.

PT Chart Field Tips

Habits that keep PT chart readings honest.

  1. 1

    Let the system settle

    Read pressures after the system has run steadily for about ten minutes. Readings right after startup or after adding refrigerant are not stable.

  2. 2

    Measure the line, not the air

    Clamp the temperature probe on clean copper and insulate it. A probe reading the air beside the line throws superheat and subcooling off by several degrees.

  3. 3

    Zero your gauges

    Check that the gauges read 0 psig when open to the air before you connect. On low-pressure refrigerants, a 2 psi error is a large temperature error.

  4. 4

    Charge blends as liquid

    Any blend with glide separates if charged as vapor. Take liquid from the cylinder and meter it in through the manifold.

Sources: ACHR News: Charging refrigeration systems with blended refrigerants, HVAC School: Glide, blends and why you can’t mix refrigerants, EPA: Section 608 refrigerant management

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