Refrigerant Superheat Calculator
Enter suction pressure and suction line temperature. Returns superheat, saturation temperature, and whether you're in the target window for fixed-orifice or TXV systems. PT data for R-410A, R-22, R-32, R-454B.
HVAC Toolkit runs this math at zero bars
Worked example
R-410A system, TXV metering. Gauge reads 130 psig at the suction service port; clamp-on thermocouple reads 52°F on the line 6 inches from the valve.
PT reference — R-410A (condensed)
| Pressure (psig) | Sat. temp (°F) | Pressure (kPa) | Sat. temp (°C) |
|---|
Values interpolated for the full range by the calculator above. Full bubble + dew data in the refrigerant PT charts.
Common mistakes
- Reading liquid-line pressure as suction. Superheat uses the low-side only. Confirm which port the hose is on.
- Confusing subcool with superheat. Subcool uses high-side pressure and liquid-line temp. Different number, different diagnostic.
- Ignoring ambient on short test runs. On a 60°F day with a hot roof, the reported superheat drifts until the system is in steady state — wait 10–15 minutes after startup.
- Using bubble-point vs dew-point on blends. R-410A has negligible glide (~0.3°F). R-454B has ~2°F glide — use dew-point for superheat, bubble-point for subcool.
FAQ
What is a normal superheat value?
TXV or EEV systems target 8–12°F at the evaporator outlet. Fixed-orifice systems target 8–20°F at the compressor, and the exact number depends on indoor wet-bulb and outdoor dry-bulb — consult the manufacturer's charging chart on the unit nameplate.
Do I measure at the evaporator or the compressor?
TXV/EEV superheat ("evaporator superheat") is measured at the evaporator outlet, before the suction line warms in the attic or service chase. Total superheat ("compressor superheat") is measured at the compressor inlet and includes suction-line heat gain — always higher than evaporator superheat.
Why do R-410A and R-454B read different superheats at the same pressure?
They have different saturation curves. R-454B runs about 1–2°F lower saturation temp than R-410A at the same pressure in the A/C range, so the same line temp yields slightly higher superheat on R-454B. Use the PT data for the actual refrigerant in the system.
Does elevation affect the reading?
The saturation relationship is absolute-pressure-based, but service gauges read gauge pressure. At 5,000 ft (atmospheric ≈ 12.2 psia), a gauge reading the same psig corresponds to a lower absolute pressure than at sea level — a 2.5 psi difference shifts R-410A SST by about 1°F. Manufacturer charging charts assume sea level unless noted.
Sources
The web page won't load where you charge the unit
HVAC Toolkit keeps R-410A/R-454B PT curves on the phone, logs each check, and exports the run for the ticket. No signal, no login. Pay once.
Related
CalcSpec is an estimator for qualified technicians. Results do not replace manufacturer charging charts, AHRI-certified gauges, or the judgment of a licensed HVAC contractor. Always follow EPA Section 608 refrigerant-handling requirements.