R-422B PT Chart
Saturation pressure for R-422B from -40°F to 140°F, with liquid (bubble) and vapor (dew) columns. Look up a pressure or temperature, switch to metric, and check typical operating pressures.
By BrazeJobs Team · Updated
R-422B Lookup
Liquid (Bubble)
69.6 psig
Vapor (Dew)
59.4 psig
Bubble Point
32.3°F
Dew Point
39.7°F
Chart range: -40°F to 140°F. Enter vacuum as a negative pressure. Check R-422B superheat and subcooling
R-422B PT Chart
| Temp | Liquid (Bubble) | Vapor (Dew) |
|---|---|---|
| -40°F | 0.9 psig | 2.7 inHg vac |
| -35°F | 3.0 psig | 0.9 inHg vac |
| -30°F | 5.4 psig | 1.1 psig |
| -25°F | 7.9 psig | 3.2 psig |
| -20°F | 10.7 psig | 5.7 psig |
| -15°F | 13.8 psig | 8.3 psig |
| -10°F | 17.1 psig | 11.3 psig |
| -5°F | 20.7 psig | 14.5 psig |
| 0°F | 24.7 psig | 18.0 psig |
| 5°F | 29.0 psig | 21.9 psig |
| 10°F | 33.6 psig | 26.1 psig |
| 15°F | 38.6 psig | 30.6 psig |
| 20°F | 43.9 psig | 35.5 psig |
| 25°F | 49.7 psig | 40.8 psig |
| 30°F | 55.9 psig | 46.6 psig |
| 35°F | 62.5 psig | 52.7 psig |
| 40°F | 69.6 psig | 59.4 psig |
| 45°F | 77.2 psig | 66.5 psig |
| 50°F | 85.3 psig | 74.1 psig |
| 55°F | 94.0 psig | 82.2 psig |
| 60°F | 103.0 psig | 90.9 psig |
| 65°F | 113.0 psig | 100.0 psig |
| 70°F | 123.0 psig | 110.0 psig |
| 75°F | 134.0 psig | 120.0 psig |
| 80°F | 145.0 psig | 132.0 psig |
| 85°F | 158.0 psig | 143.0 psig |
| 90°F | 170.0 psig | 156.0 psig |
| 95°F | 184.0 psig | 169.0 psig |
| 100°F | 198.0 psig | 183.0 psig |
| 105°F | 213.0 psig | 198.0 psig |
| 110°F | 229.0 psig | 213.0 psig |
| 115°F | 246.0 psig | 230.0 psig |
| 120°F | 263.0 psig | 247.0 psig |
| 125°F | 281.0 psig | 265.0 psig |
| 130°F | 301.0 psig | 284.0 psig |
| 135°F | 321.0 psig | 304.0 psig |
| 140°F | 342.0 psig | 326.0 psig |
About R-422B
R-422B is an HFC blend made to retrofit R-22 air conditioning and heat pumps without an oil change. A small amount of isobutane helps carry mineral oil back to the compressor.
It is zeotropic, with a glide of several degrees, so the chart has liquid (bubble) and vapor (dew) columns. Capacity is lower than R-22, so a retrofitted system may run longer to do the same work.
- Retrofit of R-22 residential and light commercial AC and heat pumps
- Systems where an oil change is impractical
R-422B Properties
Key facts for identifying R-422B and choosing tools, oil and replacements.
| Property | Value |
|---|---|
| Type | HFC |
| Composition | R-125 55%, R-134a 42%, R-600a (isobutane) 3% by weight |
| ASHRAE safety class | A1 |
| GWP (IPCC AR4) | 2,526 |
| Boiling point at 1 atm | -42.4°F |
| Critical temperature | 181.8°F |
| Oil | Works with the existing mineral oil, alkylbenzene or POE |
| Trade names | NU-22B |
| Replaces | R-22 |
| Replaced by | None |
Typical R-422B Operating Pressures
Suction pressure is the vapor (dew) pressure at the evaporator temperature; head pressure is the liquid (bubble) pressure at the condensing temperature. The temperatures are common design points, not charging targets.
| Condition | Evaporator | Suction | Condensing | Head |
|---|---|---|---|---|
| AC cooling, 95°F outdoor | 40°F | 59.4 psig | 115°F | 246.0 psig |
How to Read the R-422B PT Chart
The chart covers -40°F to 140°F. Pressures are gauge pressure (psig), the number your manifold shows; switch to °C and kPa above if you work in metric. At the cold end, R-422B saturates below atmospheric pressure, so those rows read in inches of mercury vacuum (inHg vac), the same as the vacuum scale on a compound gauge.
R-422B is a zeotropic blend, so it boils over a range of temperatures instead of at one point. That range is the glide. The liquid (bubble) column gives the pressure where the first bubble forms; the vapor (dew) column gives the pressure where the last drop of liquid boils off.
At 40°F, the bubble pressure is 69.6 psig and the dew pressure is 59.4 psig. Read the other way, at 59.4 psig the glide is about 7.3°F.
Use the vapor (dew) column for superheat on the suction line and the liquid (bubble) column for subcooling on the liquid line. Mixing them up shifts the answer by the glide.
Superheat and Subcooling Formulas
The PT chart turns a gauge pressure into a saturation temperature. Compare that with a line temperature to get superheat or subcooling.
- Tsuction
- Suction line temperature near the outdoor unit or compressor, °F
- Tliquid
- Liquid line temperature leaving the condenser, °F
- Tdew
- Dew point at suction pressure (vapor column), °F
- Tbubble
- Bubble point at liquid pressure (liquid column), °F
Gauge pressure (psig) is pressure above atmospheric. Below 0 psig, the chart shows vacuum in inches of mercury.
Worked Example: R-422B Superheat and Subcooling
AC cooling, 95°F outdoor: an R-422B system reads 59.4 psig suction with a 50°F suction line, and 246.0 psig on the liquid line with a 105°F liquid line.
- Dew point at 59.4 psig: 40.0°F.
- Superheat: 50°F − 40.0°F = 10.0°F.
- Bubble point at 246.0 psig: 115.0°F.
- Subcooling: 115.0°F − 105°F = 10.0°F.
Is R-422B Being Phased Out?
R-422B is a retrofit-only refrigerant for keeping R-22 equipment running. It is an HFC with a GWP of 2,526, so it falls under the HFC phasedown and is not used in new equipment.
Retrofits often keep the existing mineral oil, but systems with long line sets or large oil hold-up may need some POE added for oil return.
R-422B Field Tips
Practical points for working on R-422B systems, from the sources below.
Sources: ACHR News: Refrigerant allows use of mineral oil in retrofits, EPA: Choosing the right R-22 retrofit, ACHR News: R-22 retrofit round-up