Instantly look up saturation pressure or temperature for R-410A, R-22, R-32, R-134a, and R-454B. Full interactive PT chart with interpolation.
| Temp (°F) | Pressure (PSIG) |
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Shop MotorsThe pressure-temperature chart is arguably the most fundamental tool in an HVAC technician's diagnostic arsenal. It defines the saturation relationship for each refrigerant, which is the foundation for calculating superheat and subcooling — the two measurements that tell you everything about system charge and performance.
To determine superheat, you measure suction pressure, look up the corresponding saturation temperature on the PT chart, and subtract it from the actual suction line temperature. Without the PT chart, there is no way to convert a pressure gauge reading into a meaningful temperature for this calculation.
Subcooling is calculated by measuring high-side pressure, converting it to condensing saturation temperature using the PT chart, and subtracting the liquid line temperature from this saturation temperature. The PT chart is essential for this conversion.
PT charts help technicians identify non-condensable gases (air) in a system. If the measured pressure is higher than what the PT chart indicates for the measured temperature, non-condensable gases may be present. PT charts also help verify proper operating pressures for a given ambient condition and confirm that the correct refrigerant is in the system.
Different refrigerants have vastly different pressure-temperature relationships. R-410A operates at nearly double the pressure of R-22 at the same temperature. R-454B operates at pressures similar to R-410A. Understanding these differences is critical when working on or retrofitting systems, and the PT chart makes these differences immediately visible.
A refrigerant PT (pressure-temperature) chart shows the relationship between a refrigerant's pressure and its saturation (boiling/condensing) temperature. To use it: find the measured pressure on one axis and read across to find the corresponding saturation temperature, or vice versa. At saturation, the refrigerant is changing phase between liquid and vapor. Any temperature above saturation at a given pressure indicates superheat (vapor), and any temperature below indicates subcooling (liquid).
At 118 PSI gauge pressure, R-410A has a saturation temperature of approximately 40°F (4.4°C). This is a common operating suction pressure for R-410A air conditioning systems running in cooling mode. If the suction line temperature reads higher than 40°F at this pressure, the difference is the superheat.
HVAC technicians use PT charts to convert between pressure gauge readings and saturation temperatures. This conversion is essential for calculating superheat and subcooling, the two most important diagnostic measurements for evaluating refrigerant charge and system performance. PT charts are also used to determine target operating pressures, identify non-condensable gases, and verify proper system operation across different ambient conditions.
R-22 (Freon) was phased out of production in 2020 under the Montreal Protocol due to its ozone-depleting potential. Common replacements include: R-410A (the most common replacement in new residential systems, though it has high GWP), R-407C (a drop-in replacement blend for some R-22 systems), and R-454B (a next-generation A2L refrigerant with lower GWP that is replacing R-410A in new equipment). For existing R-22 systems, retrofit options include R-407C and R-422D.
R-454B (sold under brand names like Opteon XL41) is a next-generation A2L (mildly flammable) refrigerant designed to replace R-410A in residential and commercial HVAC systems. It has a significantly lower Global Warming Potential (GWP of 466 compared to R-410A's GWP of 2088), operates at similar pressures to R-410A, and provides comparable performance. R-454B is being adopted by major equipment manufacturers as the industry transitions to lower-GWP refrigerants under EPA regulations.
Gauge pressure (PSIG) measures pressure relative to atmospheric pressure, meaning 0 PSIG equals atmospheric pressure (approximately 14.7 PSI at sea level). Absolute pressure (PSIA) measures pressure relative to a perfect vacuum, so 0 PSIA is a complete vacuum. The relationship is: PSIA = PSIG + 14.7. HVAC technicians typically work with gauge pressure (PSIG), which is what standard refrigerant manifold gauges display. PT charts for HVAC use are normally listed in PSIG.
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