PT Calculator
Enter a temperature or a pressure for any refrigerant in the dataset; get the corresponding saturation value, with bubble/dew handling for zeotropic blends and ten-plus worked examples covering the full range of HVAC service scenarios.
Updated September 28, 2026
PT chart range for R-410A: −40°F to 150°F.
What the PT calculator actually computes
A PT calculator converts between refrigerant saturation pressure and saturation temperature at thermodynamic equilibrium. Pick a temperature, get the saturation pressure; pick a pressure, get the saturation temperature.
The math is direct lookup against the refrigerant's PT chart, interpolated linearly between the 1°F data points in the underlying dataset. The relationship is fundamental to vapor-compression refrigeration. Any point where liquid and vapor coexist — broadly, the evaporator and condenser — sits on the saturation curve.
Four representative refrigerants on a single PT chart, showing how saturation pressure rises with temperature. Source: CoolProp 7.2.0 saturation data, plotted over the −40°F to 130°F service range.
Pure refrigerants vs zeotropic blends — why bubble and dew matter
Pure refrigerants (R-22, R-32, R-134a, R-744) have a single saturation curve — at any pressure there is one saturation temperature. Azeotropic blends (R-507A, R-500, R-502) behave the same way because their component proportions are engineered for zero-glide behavior.
Zeotropic blends (R-407C, R-454C, R-455A, R-448A, R-449A) have two saturation curves at any pressure: bubble, where the first vapor forms when heating the liquid, and dew, where the last liquid disappears when condensing the vapor. The temperature difference between bubble and dew at the same pressure is the temperature glide.
Glide visualization for R-407C across a typical residential evaporator coil at 40°F bubble. Source: CoolProp 7.2.0 saturation data.
For service measurement, the curve selection matters. Suction-line superheat uses the dew temperature at suction pressure as the saturation reference; liquid-line subcooling uses the bubble temperature at discharge pressure. Wrong-curve selection introduces measurement error equal to the glide.
Temperature glide across common HVAC blends, measured as dew-minus-bubble at 0°C (CoolProp 7.2.0 dataset value). Pure refrigerants and azeotropes have zero glide and are omitted.
Real service problems solved with the PT chart
Ten field scenarios spanning residential AC, commercial refrigeration, chillers, mobile AC, transcritical CO2, and heat pumps. Each shows what gets measured at the manifold, the PT chart lookups that convert pressures to saturation temperatures, the derived superheat / subcooling values, and a verdict on what to do next.
Verifying R-410A charge on a 95°F day
Scenario · 3-ton residential R-410A central AC, 95°F outdoor ambient, 75°F indoor return air, TXV metering device. The system has been running 20 minutes at steady state and you want to confirm charge before signing off.
Spotting an R-410A undercharge after a leak repair
Scenario · Same 3-ton residential R-410A system, just back from a leak repair at the evaporator. You suspect the recharge wasn't complete and want to confirm before the customer calls back when the weather warms up.
Catching an R-410A overcharge from a prior service add
Scenario · Same 3-ton residential R-410A system. A previous tech topped off by gauge feel rather than by weight. The compressor is running noisy and the customer is reporting higher power bills.
Charging a wide-glide R-454C walk-in freezer
Scenario · R-454C walk-in freezer, −20°F target evaporator temperature, 95°F ambient. R-454C has roughly 14°F glide so curve selection matters: dew at suction for superheat, bubble at discharge for subcooling.
Pressure-envelope check for an R-22 to R-407C retrofit
Scenario · Existing R-22 residential AC under consideration for R-407C retrofit. Customer wants to know: will the existing manifold gauges, hoses, and line set handle R-407C, or does the equipment need replacement?
| Refrigerant | 40°F | 70°F | 95°F | Δ vs R-22 |
|---|---|---|---|---|
| R-22 | 69 | 121 | 182 | baseline |
| R-407C bubble | 80 | 141 | 209 | +15% |
| R-407C dew | 63 | 117 | 181 | 0% |
Will R-410A service tools handle a new R-32 system?
Scenario · A homeowner is replacing an R-410A condenser with a new R-32 system. The field tech asks the practical question: do I need new manifold gauges, hoses, recovery cylinders for R-32, or can my existing R-410A gear stay?
| Refrigerant | 40°F | 70°F | 95°F | Δ vs R-410A |
|---|---|---|---|---|
| R-410A | 119 | 202 | 296 | baseline |
| R-32 | 121 | 206 | 303 | +2% |
Diagnosing a struggling R-134a centrifugal chiller
Scenario · Water-cooled R-134a centrifugal chiller. Operator reports the chiller has trouble making its 45°F leaving chilled water setpoint despite 85°F entering condenser water. You take manifold and liquid line readings.
Hot-day R-1234yf mobile AC verification
Scenario · 2020+ model year vehicle with R-1234yf MAC system. 100°F ambient, AC at max cooling, vehicle stationary in a parking lot. Customer says the cabin doesn't get cold enough; you hook up MAC manifold gauges.
Reading an R-744 transcritical supermarket system
Scenario · Supermarket R-744 transcritical commercial refrigeration system at 95°F outdoor — above CO2 critical temperature (87.8°F). Medium-temp and low-temp evaporator circuits feed a single high-pressure gas cooler.
Reading an R-410A heat pump in heating mode at 30°F outdoor
Scenario · R-410A residential air-source heat pump in heating mode. 30°F outdoor (outdoor coil is now the evaporator), 70°F indoor return air (indoor coil is now the condenser). Customer reports the unit runs but the home doesn't feel warm.
Operating pressure ranges by refrigerant — quick reference table
Typical operating pressure ranges across major refrigerants and applications. These are field-service reference ranges, not exact values — actual operating pressures depend on charge, ambient, load, superheat, subcooling, and equipment-specific conditions.
| Refrigerant | Application | Suction PSIG | Discharge PSIG |
|---|---|---|---|
| R-410A | Residential AC, 95°F ambient | 114-130 | 366-419 |
| R-32 | Residential AC, 95°F ambient | 116-133 | 375-429 |
| R-454B | Residential AC, 95°F ambient | 103-118 | 346-396 |
| R-22 | Residential AC (legacy), 95°F ambient | 66-76 | 226-260 |
| R-407C | R-22 retrofit AC, 95°F ambient | 60-71 | 260-299 |
| R-404A | Low-temp commercial, −20°F evap, 95°F ambient | 14-18 | 273-333 |
| R-448A | Low-temp commercial retrofit, −20°F evap, 95°F ambient | 8-12 | 281-343 |
| R-454C | Low-temp commercial, −20°F evap, 95°F ambient | 6-9 | 255-311 |
Suction and head are computed from the CoolProp-verified PT dataset (dew and bubble saturation via satPressure, rounded to whole PSIG): residential = dew pressure of a 38–45°F evaporator with head 15–25°F above ambient; commercial = dew pressure within ±3°F of the listed evaporator with head 15–30°F above ambient. Actual gauge readings vary with charge, load, and equipment condition. R-744 (sub-critical + transcritical CO₂), R-290 heat pump, R-717 (ammonia) industrial, R-134a and R-513A chillers, and R-1234yf mobile A/C are omitted — their operating-pressure method isn't defined in the dataset-computed model yet.
Saturation pressure quick reference — common service temperatures
Saturation pressure values at common service temperatures across mainstream refrigerants. All values are PSIG from CoolProp 7.2.0. For zeotropic blends, bubble / dew values shown.
| Refrigerant | 32°F | 45°F | 70°F | 95°F | 120°F |
|---|---|---|---|---|---|
| R-22 | 58 | 76 | 121 | 182 | 260 |
| R-410A | 101 | 131 | 202 | 296 | 419 |
| R-32 | 103 | 133 | 206 | 303 | 429 |
| R-454B | 96/91 | 123/118 | 191/183 | 280/270 | 396/384 |
| R-134a | 28 | 40 | 71 | 114 | 171 |
| R-404A | 74 | 96 | 149 | 220 | 312 |
| R-407C | 68/52 | 89/71 | 141/117 | 209/181 | 299/266 |
| R-454C | 70/51 | 91/69 | 141/112 | 207/171 | 292/249 |
| R-744 | 491 | 594 | 838 | transcritical | transcritical |
| R-290 | 54 | 71 | 110 | 162 | 228 |
| R-717 | 48 | 66 | 114 | 181 | 272 |
Computed live from the CoolProp 7.2.0 PT dataset via satPressure() — bubble (saturated liquid) shown for pures; bubble/dew for zeotropic blends; “transcritical” where the temperature is above the fluid's critical point. For exact values at any temperature, use the calculator above.
Saturation pressure at 95°F across mainstream refrigerants, descending — visual companion to the quick-reference table. Zeotropic blends shown at bubble pressure. R-744 (CO2) is transcritical at 95°F and omitted (no saturation state above 87.8°F).
Common PT lookup mistakes — and how to avoid them
PT calculator results can mislead service decisions when applied incorrectly. The five most common mistakes:
- PSIG vs PSIA confusion. Service manifold gauges read PSIG; the PT calculator uses PSIG by default. Confusing the two introduces a 14.696 PSI offset (PSIA = PSIG + 14.696 at sea level, slightly less at altitude).
- Wrong curve on zeotropic blends. Using bubble pressure for superheat measurement on R-407C, R-454C, R-455A introduces error equal to the glide (11-22°F). Always use the dew curve for superheat (suction line), the bubble curve for subcooling (liquid line). Pure refrigerants and azeotropes have a single curve, so this concern does not apply.
- Saturation pressure is not operating pressure. The PT calculator gives saturation pressure at thermodynamic equilibrium. Actual operating pressure on a running system depends on charge, ambient, load, superheat, subcooling, and line pressure drop. Saturation is the reference; operating values vary around it.
- Extrapolating beyond chart range. The calculator returns "out of range" outside the chart's valid temperature range — this is correct physics, not a bug. R-744 has no saturation state above 87.8°F (its critical point); other refrigerants have similar validity limits at extremes.
- Ignoring line pressure drop. The pressure at the manifold service port differs slightly from the pressure at the compressor or evaporator due to line pressure drop. For most residential applications the drop is small and ignorable; for long line sets, large commercial systems, or systems with substantial filter-drier pressure drop, the effect is more meaningful. Account for line losses when interpreting manifold readings against design conditions.
Pressure unit conversions reference
The PT calculator supports °F / PSIG and °C / kPa unit pairs. Other pressure unit conversions are sometimes needed in HVAC service:
| From | To | Multiplier |
|---|---|---|
| PSIG | PSIA | plus 14.696 (at sea level) |
| PSIG | kPa (gauge) | times 6.8948 |
| PSIG | bar (gauge) | times 0.06895 |
| PSIG | inHg vacuum (below atmospheric) | times negative 2.036 |
| kPa (gauge) | kPa (absolute) | plus 101.325 |
| bar | PSIG | times 14.504 |
| MPa | PSIG | times 145.04 |
| Pa | kPa | divided by 1000 |
For temperature conversions: °F = (°C times nine over five) plus 32; °C = (°F minus 32) times five over nine. The calculator handles both temperature units automatically; this conversion table is for reference when reading equipment data plates in unfamiliar units.
When to use this calculator vs the others
The PT calculator is the foundational lookup tool. Other calculators on the site build on PT lookups for specific service tasks:
- PT Calculator (this page) — pressure-temperature lookup, either direction, for any refrigerant. Use for quick reference, retrofit comparison, or as a building block in manual calculations.
- Superheat Calculator — adds suction-line temperature input, computes superheat with automatic dew/bubble curve selection. Use for charging fixed-orifice systems or for diagnostic superheat measurement on any system.
- Subcooling Calculator — adds liquid-line temperature input, computes subcooling with automatic curve selection. Use for charging TXV systems or for diagnostic subcooling measurement.
- Combined SH/SC/PT Calculator — both suction and liquid line inputs, computes superheat and subcooling together, displays diagnostic pattern banner (undercharge/overcharge/restriction/airflow).
- PT Comparison Tool — overlays 2-4 refrigerants' PT curves on a single chart. Use for retrofit pressure-envelope comparison.
- Retrofit Compatibility Calculator — pair comparison covering lubricant compatibility, safety class, pressure envelope, and glide. Use for retrofit decision-making beyond just pressure comparison.
Sources behind the calculator data
All saturation values come from primary references with documented provenance:
- CoolProp 7.2.0 (Bell, Wronski, Quoilin, Lemort 2014, doi:10.1021/ie4033999) — REFPROP-compatible Helmholtz EOS implementation. Source for 51 fluids: pure refrigerants (R-22, R-32, R-134a, R-744, etc.) and CoolProp's predefined mixtures (R-410A, R-407C, R-404A, etc.).
- CoolProp 8.0.0 — same Helmholtz EOS engine, newer release. Source for 6 lower-GWP fluids CoolProp 7.2.0 did not yet ship, including R-450A, R-514A, R-515A, R-515B, R-1224yd(Z), and the pure HFO R-1336mzz(Z).
- Manufacturer technical datasheets — for the 2 R-404A retrofit blends CoolProp does not model: R-438A (Chemours ISCEON MO99) and R-448A (Honeywell Solstice N40). The published PT tables are cited on each refrigerant's detail page.
- ASHRAE Standard 34-2022 — Designation and Safety Classification of Refrigerants. Source for composition specifications and safety class assignments.
- ASHRAE Handbook—Refrigeration (2022) — Application context, operating range references, service procedure guidance.
Each refrigerant's detail page (linked from the dropdown) cites the specific data source for that refrigerant's PT chart.
How to read your results
- Saturation pressure (PSIG or kPa)
- In the temperature-to-pressure direction, this is the gauge pressure at which a pure refrigerant boils or condenses at the temperature you entered. It is the thermodynamic reference a manifold should read at that saturation temperature; actual operating pressure varies with charge, ambient, load, and line drop. PSIG is gauge (PSIA = PSIG + 14.696 at sea level); kPa shown is gauge above 101.325 kPa atmospheric.
- Saturation temperature (°F or °C)
- In the pressure-to-temperature direction, this is the temperature at which a pure refrigerant boils or condenses at the gauge pressure you entered. Subtract it from a measured suction-line temperature to get superheat, or subtract a measured liquid-line temperature from it to get subcooling.
- Bubble value (bubble pressure or bubble temperature)
- Shown only for zeotropic blends. The bubble point is the saturated-liquid side, where the first vapor bubble forms. Use the bubble curve for liquid-line subcooling on blends; using it for superheat introduces error equal to the glide.
- Dew value (dew pressure or dew temperature)
- Shown only for zeotropic blends. The dew point is the saturated-vapor side, where the last liquid droplet evaporates. Use the dew curve for suction-line superheat on blends; the superheat calculator selects it automatically.
- Glide
- The spread between the bubble and dew values at your entered condition, displayed in the active pressure or temperature unit. Near-zero for pure refrigerants, azeotropes, and near-azeotropes like R-410A means the two curves coincide; a large glide (R-407C, R-454C) means curve selection materially changes superheat and subcooling results.
- Out-of-range and no-data messages
- “Outside the chart range” means the entered value falls beyond the refrigerant’s validated −40°F to 150°F table or above its critical point (for example R-744 above 87.8°F), where no saturation state exists — this is correct physics, not an error. “No PT data available” appears for manual-blend refrigerants that have no computed chart.
- PT chart range reference
- Below the result, the tool states the valid temperature span for the selected refrigerant and, for zeotropic blends, the dataset glide at 0°C. Confirm your input sits inside the modeled range before trusting the result.
How to use this calculator
- Pick a refrigerant from the dropdown. Defaults to R-410A.
- Choose direction: 'Pressure from temperature' (PT chart lookup) or 'Temperature from pressure' (inverse).
- Adjust unit toggles if you need metric values (°C / kPa).
- Enter your value and click Calculate. The result shows both bubble and dew for zeotropic blends.
- Cross-reference against the equipment data plate and the worked examples below to interpret the result for your specific scenario.
Common errors
- Confusing PSIG (gauge) with PSIA (absolute). Manifold gauges read PSIG; PSIA = PSIG + 14.696.
- Using the bubble pressure for superheat math on a zeotropic blend — use the dew pressure instead. The superheat calculator handles this automatically when a zeotropic blend is selected.
- Treating saturation pressure as operating pressure. Saturation is the thermodynamic reference; operating pressure depends on charge, ambient, load, superheat, and subcooling.
- Extrapolating beyond the chart range. R-744 has no saturation state above 87.8°F (the critical temperature); the calculator returns 'out of range' rather than producing a fabricated value.
Underlying math
Formula
P_sat = f(T) or T_sat = f(P) Linear interpolation between adjacent 1°F data points in the refrigerant's PT chart. For zeotropic blends, both bubble (saturated liquid) and dew (saturated vapor) curves are interpolated independently.
Source
Saturation pressures from CoolProp — 51 fluids on CoolProp 7.2.0 (Bell, Wronski, Quoilin, Lemort 2014, doi:10.1021/ie4033999) and 6 newer low-GWP fluids on CoolProp 8.0.0, both REFPROP-compatible Helmholtz EOS. The 2 manufacturer-datasheet fluids (R-438A, R-448A) come from the named manufacturer PT charts cited on each refrigerant's detail page.
Worked example
R-410A at 70°F: CoolProp returns P_bubble = 201.76 PSIG, P_dew = 201.07 PSIG (0.7 PSI glide — near-azeotropic). R-407C at 70°F: CoolProp returns P_bubble = 140.52 PSIG, P_dew = 117.29 PSIG (23 PSI glide — significant zeotrope). R-744 (CO2) at 70°F: P_sat = 838.13 PSIG. Above 87.8°F (the critical point) no saturation state exists and the chart truncates. R-32 at 95°F: 302.9 PSIG saturation. R-410A at 95°F: 296.4 PSIG. R-32 runs about 2% higher than R-410A, consistent across the operating envelope.
Related tools
Superheat Calculator
Suction-line PSIG plus measured °F to superheat, with diagnostic context.
Subcooling Calculator
Liquid-line PSIG plus measured °F to subcooling.
Combined SH/SC/PT
Both sides plus pattern-matching diagnostic banner in one workflow.
PT Comparison Tool
Overlay 2-4 refrigerants' PT curves for side-by-side comparison.
Retrofit Compatibility
Pair comparison: lubricant, safety class, pressure envelope, glide.
Frequently asked
›What's the difference between PSI, PSIG, and PSIA?
PSI is a generic pressure unit (pounds per square inch). PSIG is gauge pressure — pressure above atmospheric (0 PSIG = 14.696 PSIA at sea level). PSIA is absolute pressure measured from a perfect vacuum. Service manifold gauges read in PSIG. All values on this calculator and across hvacptcharts.com are PSIG unless explicitly stated as PSIA. Convert with PSIA = PSIG + 14.696.
›Why do some refrigerants show two pressures (bubble and dew)?
Zeotropic blends boil and condense across a temperature range at constant pressure rather than at a single temperature. The bubble pressure is the saturation pressure of the liquid (where vapor first forms); the dew pressure is the saturation pressure of the vapor (where the last liquid disappears). The temperature difference at the same pressure is the glide. For pure refrigerants (R-22, R-134a, R-32) and azeotropes (R-507A, R-500) the two values coincide.
›How accurate is the calculator?
Saturation pressures come from CoolProp, a REFPROP-compatible Helmholtz-energy EOS: CoolProp 7.2.0 for 51 fluids and CoolProp 8.0.0 for 6 newer low-GWP fluids (including R-450A and the pure HFO R-1336mzz(Z)). The remaining 2 refrigerants — R-438A (Chemours ISCEON MO99) and R-448A (Honeywell Solstice N40) — are transcribed from the named manufacturer PT charts and match the source datasheet.
›What temperature range does the calculator cover?
Default coverage is −40°F to 150°F at 1°F increments — 191 data points per refrigerant. Sub-critical refrigerants are truncated at their critical temperature where no saturation state exists. R-744 (CO2) stops at 87°F (critical temperature 87.8°F); R-13 at 84°F; R-1150 (ethylene) at 48°F. Outside the chart range the calculator returns 'out of range' rather than extrapolating values that don't correspond to physical saturation.
›Can I get PT values in metric units?
Yes — toggle the unit set to °C / kPa. The kPa values are gauge (kPa above atmospheric, where atmospheric is 101.325 kPa). For absolute kPa, add 101.325. The calculator handles both unit systems with the same underlying CoolProp data.
›How does this PT calculator differ from the superheat and subcooling calculators?
The PT calculator does pressure-to-temperature lookup in either direction — it answers 'what's the saturation pressure at this temperature?' or 'what's the saturation temperature at this pressure?' The superheat and subcooling calculators add the line-temperature input and compute the temperature difference: superheat = suction line temperature − saturation temperature at suction pressure (using the dew curve for blends); subcooling = saturation temperature at discharge pressure (bubble curve for blends) − liquid line temperature.
›Why do operating pressures differ from saturation pressures?
Saturation pressure is the thermodynamic equilibrium pressure at a given temperature. Operating pressure on a running system depends on refrigerant charge, ambient temperature, indoor load, superheat, subcooling, and line pressure drop. The PT chart gives the reference value; actual gauge readings on a running system vary around the saturation reference based on these operating factors.
›Can I use the calculator for retrofit decisions?
Yes — the PT calculator is useful for understanding the pressure envelope of candidate retrofit refrigerants relative to the original equipment design. Compare R-22 saturation values to R-407C bubble/dew values to see the retrofit pressure delta. Compare R-410A to R-32 saturation to confirm the small (~2%) pressure increase that R-32 introduces. For pair comparisons with full retrofit guidance, use the refrigerant comparison and retrofit compatibility tools.