Use the refrigerant on the unit's nameplate.
High side gauge at the liquid service port.
Clamp probe on the liquid line near the outdoor unit.
Formula: subcooling = condenser saturation temperature at the liquid pressure minus the liquid line temperature.
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 subcooling
10.1°F
90.0°F on the line against 100.1°F saturation at 319.0 psig.
- Condenser saturation temperature
- 100.1°F
- Liquid line temperature
- 90.0°F
- Subcooling
- 10.1°F
- PT chart point used
- Bubble point (liquid column)
PT chart
Liquid side PT chart
Saturation pressure in psig at condensing temperatures. The blends use the liquid (bubble) column.
| Saturation temp | R-410A liquid | R-454B liquid | R-32 | R-22 |
|---|---|---|---|---|
| 80°F | 236.5 | 225.6 | 241.5 | 143.6 |
| 84°F | 251.6 | 239.9 | 256.9 | 153.2 |
| 88°F | 267.3 | 254.8 | 273.0 | 163.2 |
| 92°F | 283.6 | 270.4 | 289.8 | 173.7 |
| 96°F | 300.7 | 286.6 | 307.4 | 184.6 |
| 100°F | 318.6 | 303.6 | 325.7 | 195.9 |
| 105°F | 341.9 | 325.7 | 349.6 | 210.8 |
| 110°F | 366.4 | 348.9 | 374.9 | 226.4 |
| 115°F | 392.3 | 373.4 | 401.4 | 242.8 |
| 120°F | 419.4 | 399.1 | 429.3 | 260.0 |
| 125°F | 447.9 | 426.0 | 458.7 | 278.0 |
| 130°F | 477.9 | 454.2 | 489.5 | 296.9 |
How it works
How to calculate subcooling
1. Let it run.Run the system in cooling mode for at least 15 minutes before you check the charge, as Bryant's procedure asks.
2. Read the liquid side. Take the pressure at the liquid service port and the liquid line temperature near the outdoor coil.
3. Look up saturation. The subcooling calculator finds the pressure on the chart for the refrigerant you picked and reads the condensing temperature, interpolating in a straight line between rows. For R-410A and R-454B it reads the liquid (bubble) column.
4. Subtract. Saturation temperature minus liquid line temperature is the subcooling. A negative answer means the line reads warmer than saturation, so check the gauge, the probe and the refrigerant first.
5. Compare with the data plate. Subcooling is the charging guide on TXV systems; on a fixed orifice system use the superheat calculator and the unit's superheat table. If you are checking whether the system was sized right in the first place, the AC tonnage calculator gives a rule of thumb figure.
Questions
What HVAC techs ask about this
How do you calculate subcooling?
What should subcooling be?
Where do I take the liquid line readings?
Is subcooling too low a sign to add refrigerant?
Why does the subcooling calculator use the bubble point?
What temperature is R-22 at 196 psig?
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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