If you only keep five R-410A numbers in your head, make them these: 101 psig at 32 °F, 118 at 40 °F, 143 at 50 °F, 318 at 100 °F and 419 at 120 °F. Anything in between takes a few seconds on the R-410A PT chart.
All five are saturation pressures. They tell you what temperature the refrigerant is boiling or condensing at for a given gauge reading. They aren't targets. None of them says the charge is right.
The five rows, both columns
| Saturation temp (°F) | Bubble (psig) | Dew (psig) |
|---|---|---|
| 32 | 101.4 | 101.1 |
| 40 | 118.8 | 118.4 |
| 50 | 143.2 | 142.6 |
| 100 | 318.5 | 317.6 |
| 120 | 419.4 | 418.3 |
Reference only. Check the equipment data plate and the manufacturer's charging data, and verify with your gauges.
R-410A is a blend, so the chart has two columns. But look how close they are. The gap is 0.3 psi at 32 °F and about 1 psi at 120 °F, which is why many pocket cards and gauge faces show R-410A as a single scale. Don't carry that habit over to R-448A. At 40 °F its bubble and dew sit about 17 psi apart.
Why these five
32 °F is where water freezes. A suction reading under about 101 psig means the refrigerant is boiling at or below roughly 32 °F, cold enough that the coil can start to frost. That's the one row I'd want to know without reaching for my phone.
40 and 50 bracket the suction readings I'd expect to see most on comfort cooling. That's a judgment call, not a rule. The equipment data decides what's normal for the unit in front of you.
100 and 120 are for the high side. A liquid line gauge reading 318 psig means roughly 100 °F condensing. At 419 you're near 120 °F, and you'll probably want to know why.
Using one of them on a real reading
Say the suction gauge reads 118 psig and the suction line clamp says 52 °F. Read the dew column. 118 psig is 39.8 °F saturated, so superheat is 12.2 °F. On the liquid side, 320 psig is 100.3 °F on the bubble column. With the liquid line at 94 °F, that's 6.3 °F of subcooling.
Whether 12 °F of superheat or 6 °F of subcooling is right depends on the metering device and the manufacturer's charging chart. The chart can't tell you that. If you'd rather not do the subtraction on a roof, the superheat and subcooling calculator picks the right column for you.
What to look up every time
Everything else. Memory is fine for a quick sanity check, the kind where you glance at the gauges and know something is off before the clamps are on, but it isn't good enough for a number that goes on a service report.
And guessing between rows gets worse the higher you go. Near 40 °F, a 5 °F step on the dew column is about 12 psi (118.4 to 130.1). Near 100 °F, the same 5 °F step is about 23 psi (317.6 to 340.9). Split the difference by eye on the high side and you can be a couple of degrees out without noticing.
If you'd rather not memorize anything, the printable PT chart fits R-410A and up to five other refrigerants on one landscape page.