Refrigerant Superheat & Subcooling Calculator
Superheat and subcooling from your gauge readings, using saturation pressure-temperature data for R-410A, R-22, R-32, and R-454B.
Suction side (superheat)
Liquid side (subcooling)
How this is calculated
A refrigerant boils and condenses at a fixed temperature for any given pressure — its saturation temperature. Comparing your measured line temperature against that saturation point tells you how far from saturation the refrigerant actually is:
Superheat = suction line temp − suction saturation temp
Subcooling = liquid saturation temp − liquid line temp
Saturation temperature for a given pressure is read from the refrigerant's pressure-temperature (PT) table, interpolating between the nearest listed points when your gauge reading falls between them.
R-410A saturation PT table (reference)
| °F | psig |
|---|---|
| -20 | 26.1 |
| -10 | 36.3 |
| 0 | 48.3 |
| 10 | 62.4 |
| 20 | 78.7 |
| 30 | 97.5 |
| 40 | 118.9 |
| 50 | 143.3 |
| 60 | 170.7 |
| 70 | 201.7 |
| 80 | 236.2 |
| 90 | 274.9 |
| 100 | 317.7 |
| 110 | 365.5 |
| 120 | 417.9 |
| 130 | 476 |
In-depth guide: Superheat and subcooling: what they are and how to calculate them
How this calculator works
Measured superheat and subcooling from gauge readings, using pressure–temperature tables for R-410A, R-22, R-32 and R-454B (midpoint of the glide for R-454B).
Worked example
An R-410A system reading 118 psig on the suction line with the suction line at 50°F, and 340 psig on the liquid line with the liquid line at 95°F.
At 118 psig, R-410A saturates at about 39.6°F, so superheat = 50 − 39.6 = 10.4°F. At 340 psig it saturates at about 104.7°F, so subcooling = 104.7 − 95 = 9.7°F.
Compare those values against the manufacturer's target for that unit and conditions before adding or removing refrigerant.
Frequently asked questions
What is superheat?
Superheat is how many degrees the suction vapor is above its boiling (saturation) temperature at the measured pressure. It shows how completely the evaporator is being fed.
What is subcooling?
Subcooling is how many degrees the liquid line is below its condensing (saturation) temperature. It is the main charging check on systems with a TXV or EEV metering device.
Which do I charge by, superheat or subcooling?
Fixed-orifice (piston) systems are usually charged by superheat; TXV and EEV systems by subcooling. Always follow the unit's charging chart.
What is a normal superheat or subcooling value?
It depends on the equipment and the indoor and outdoor conditions. Many TXV systems target roughly 8–12°F subcooling, but the manufacturer's data plate or chart is the only correct target.
Common mistakes
- Charging a TXV system by superheat. A thermostatic expansion valve holds superheat roughly constant, so systems with a TXV are charged by subcooling. Fixed-orifice systems are charged by superheat.
- Measuring in the wrong place. Take pressure and temperature at the same point: suction line for superheat, liquid line leaving the condenser for subcooling.
- Reading before the system settles. Let the system run until pressures and line temperatures stop drifting before you record them.
- Mixing gauge and absolute pressure. This calculator expects gauge pressure (psig or bar gauge). An absolute reading shifts the saturation temperature.
What it does not cover
Manufacturer target superheat and subcooling, which depend on the metering device and conditions.
Sources
- ACHR News, Charging methods for metering devices
- Copeland refrigerant slider (pressure–temperature data)
Sources, checks and limits for this calculator →
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