Use the refrigerant on the unit's nameplate.
Low side gauge at the suction (vapor) service port.
Clamp probe on the suction line near the service valve, insulated.
Formula: superheat = suction line temperature minus the evaporator saturation temperature at the suction pressure.
Compare the answer with the target on the unit's data plate or the manufacturer's charging chart, not a number from the internet.
R-410A superheat
10.2°F
50.0°F on the line against 39.8°F saturation at 118.0 psig.
- Evaporator saturation temperature
- 39.8°F
- Suction line temperature
- 50.0°F
- Superheat
- 10.2°F
- PT chart point used
- Dew point (vapor column)
PT chart
Suction side PT chart
Saturation pressure in psig at evaporator temperatures. The blends use the vapor (dew) column.
| Saturation temp | R-410A vapor | R-454B vapor | R-32 | R-22 |
|---|---|---|---|---|
| 20°F | 78.4 | 70.9 | 80.0 | 43.1 |
| 24°F | 85.5 | 77.5 | 87.3 | 47.6 |
| 28°F | 93.1 | 84.4 | 95.1 | 52.4 |
| 32°F | 101.1 | 91.8 | 103.2 | 57.5 |
| 36°F | 109.5 | 99.5 | 111.8 | 62.9 |
| 40°F | 118.4 | 107.7 | 121.0 | 68.6 |
| 44°F | 127.7 | 116.3 | 130.5 | 74.5 |
| 48°F | 137.5 | 125.4 | 140.6 | 80.8 |
| 52°F | 147.9 | 134.9 | 151.2 | 87.4 |
| 56°F | 158.7 | 144.9 | 162.4 | 94.4 |
| 60°F | 170.1 | 155.4 | 174.0 | 101.6 |
How it works
How to calculate superheat
1. Let it run.Bryant's charging procedure asks for at least 15 minutes of running in cooling mode before you check the charge.
2. Read the suction pressure at the vapor service port, and the suction line temperature with an accurate thermistor or electronic thermometer on the line near the service valve, insulated from the air.
3. Look up saturation. The superheat calculator finds the pressure on the chart for the refrigerant you picked and reads the temperature, interpolating in a straight line between rows. For R-410A and R-454B it reads the vapor (dew) column.
4. Subtract. Suction line temperature minus saturation temperature is the superheat. A negative answer means a reading is off, so check the gauge, the probe and the refrigerant before you touch the charge.
5. Compare with the target.The target comes from the manufacturer. On a fixed orifice system it depends on the outdoor dry bulb and the indoor wet bulb, read from the unit's charging table. On a TXV system charge by subcooling instead, with the subcooling calculator. Sizing a new system first? Start with the AC tonnage calculator.
Questions
What HVAC techs ask about this
How do you calculate superheat?
What should superheat be?
Superheat or subcooling: which one do I charge by?
What temperature is R-410A at 118 psig?
Why does the superheat calculator use the dew point for R-454B?
Can I use the R-410A numbers on an R-32 or R-454B system?
Sources
Where the numbers come from
- Daikin Comfort Technologies North America, A1 vs. A2L Pressure Temperature Chart, USA (°F/psig), PM-A2LPTC-USA_04-24, values by Weitron. Every saturation pressure and temperature on this page and in the calculator, with liquid and vapor columns for R-410A and R-454B, and the EPA SNAP note on A2L refrigerants
- Bryant / Day & Night, 1997 Piston Guide for Residential Split-Systems, form AP01 02-10. The superheat and subcooling charging methods: superheat for non TXV metering devices, subcooling for TXV units, 15 minutes of running, where to take each reading, the required subcooling from the rating plate
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