TradeToolsHVAC · in the TradeTools app
Superheat and Subcooling Calculator
Charge check from the suction and liquid readings: the saturation temperature comes from the refrigerant's P-T table, superheat and subcooling follow, and the app flags readings outside the usual operating range.
P-T tables · R-22 to R-717
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Worked example
R-410A on a TXV: 118 psig and 55 °F on the suction line — normal?
| Refrigerant | R-410A |
|---|---|
| Metering device | TXV |
| Suction | 118 psig, line temperature 55 °F |
| Liquid | 365 psig, line temperature 95 °F |
| Superheat | 15.4 °F — normal |
|---|---|
| Saturation temperature, suction | 39.6 °F |
| Subcooling | 14.7 °F — normal |
| Saturation temperature, liquid | 109.7 °F |
At 118 psig R-410A saturates at 39.6 °F, so a 55 °F suction line is 15.4 °F of superheat. At 365 psig it saturates at 109.7 °F; a 95 °F liquid line is 14.7 °F of subcooling. Both are inside the range the app treats as normal — 5 to 20 °F superheat, 3 to 20 °F subcooling. The target for your unit is on the manufacturer's charging chart.
How it's calculated
The table behind the number
Superheat is the suction line temperature minus the saturation temperature at suction pressure; subcooling is the saturation temperature at liquid pressure minus the liquid line temperature. Saturation temperatures come from the refrigerant's pressure–temperature table (NIST REFPROP-grade data, cross-checked against manufacturer charts). For glide blends — R-454B, R-407C, R-404A — the app uses the dew point for superheat and the bubble point for subcooling; R-410A's glide is under 0.3 °F, so one table serves both sides.
- Pressure–temperature tablesR-22, R-410A, R-454B, R-32, R-407C, R-134a, R-404A, R-507A, R-290, R-717
- Manufacturer charging chartTarget superheat (fixed orifice) and target subcooling (TXV) for the specific equipment
Questions
Before you trust the number
TXV or fixed orifice — which number matters?
TXV systems are charged by subcooling, fixed-orifice systems by superheat. The app shows both and marks the metering device you selected.
Why is there no dew/bubble split for R-410A?
R-410A's temperature glide is under 0.3 °F, so one saturation table is accurate for both sides. The split matters for glide blends such as R-454B, R-407C and R-404A, where the app applies it.