R-410A pressure chart, with R-454B

What an R-410A pressure chart tells you

An R-410A pressure chart lists the pressure at which the refrigerant boils or condenses at each temperature. Inside the evaporator and the condenser, where liquid and vapour sit together, pressure and temperature are locked to each other: read one on the gauge and the chart gives you the other. That paired figure is the saturation temperature, and it is the starting point of every charge check.

The chart is only true where the refrigerant is boiling or condensing. By the time vapour reaches the suction service valve it has picked up superheat, and by the time liquid reaches the liquid-line valve it has given up subcooling — which is exactly why the gauge pressure and a line thermometer disagree, and why the difference is worth measuring.

Where these numbers come from

The R-410A columns are transcribed digit for digit from Arkema's published Forane 410A saturation chart, which lists liquid and vapor pressure in psig for every whole degree from -49 to 150 °F. The R-454B columns come from Chemours' Opteon XL41 property tables, which publish absolute pressure (psia); the gauge figures here are those values less 14.696 psia, the one-atmosphere figure the same document uses. Both makers generated their tables from NIST's REFPROP database. The lookup interpolates between whole degrees, so it never invents a curve of its own.

Sources: Arkema, Forane 410A Saturation Pressure-Temperature Data (psig) (read 2026-10-18) · Chemours, Thermodynamic Properties of Opteon XL41 (R-454B), Engineering Units (read 2026-10-18)

Bubble or dew: which R-454B column to read

R-410A is a near-azeotrope: at 118 psig its liquid and vapor columns sit only 0.2 °F apart, so either column gives the same answer at the gauge. R-454B is a zeotropic blend. At the same 118 psig its bubble point is 42.7 °F and its dew point is 45.1 °F — a glide of about 2.4 °F, and big enough to wreck a charge reading if you take the wrong column.

How to use the chart

1. Pick the refrigerant on the nameplate. The two charts are not interchangeable.
2. Choose the gauge you are reading: suction for the low side, liquid line for the high side.
3. Type the gauge pressure. The large figure is the saturation temperature from the right column.
4. Subtract: line temperature minus saturation for superheat, saturation minus line temperature for subcooling.
5. Compare against the target on the unit's own charging chart — or let the superheat and subcooling calculator do steps 4 and 5 and give the charge verdict.

Worked example on R-410A

On a TXV system the subcooling decides the charge; on a fixed orifice, superheat does. If the suction pressure is low, check airflow before blaming the charge — a clogged filter or crushed return reads exactly like an undercharge. The static pressure calculator rules that out in five minutes, and the AC not cooling decision list walks the rest of the diagnosis.

R-410A against R-454B, side by side

At any given temperature R-454B runs a little below R-410A, and the gap widens on the high side. Close enough to look familiar on a manifold, far enough to misjudge a charge by several degrees if you read an R-454B system off an R-410A chart. The R-454B transition guide covers what else changes with the new equipment; the maintenance checklist has a line for recording both pressures at every visit.

Before you connect a manifold

The refrigerant change itself is policy: epa's technology transitions programme under the aim act sets sector and subsector limits on hfc use in refrigeration, air conditioning and heat pumps. R-454B carries a global warming potential of 466 on the IPCC AR4 basis its maker quotes. Its critical temperature is 172.6 °F: above it there is no liquid and no saturation pressure, so no PT chart can run past that point.

Sources: US EPA, Stationary Refrigeration and Air Conditioning (read 2026-09-04) · US EPA, Technology Transitions (page last updated 2025-12-03) (read 2026-09-04) · Chemours, Thermodynamic Properties of Opteon XL41 (R-454B), Engineering Units (read 2026-10-18)