BOTANVÈSuperheat Calculator
Enter suction pressure and line temperature; the calculator converts pressure to saturated temperature and returns superheat with a diagnostic note.
What superheat tells you
Superheat is the number of degrees the refrigerant vapour has been heated above its saturation (boiling) temperature at the measured suction pressure. It confirms that all the liquid has boiled off in the evaporator before reaching the compressor — the single most important protection for a scroll compressor, which cannot tolerate liquid slugging. To measure it: read suction pressure at the service port, convert it to saturated temperature using the pressure–temperature relationship for the refrigerant (this calculator does that for R410A, R22 and R134a), measure the actual suction-line temperature with a clamp thermometer at the same point, and subtract.
| Reading | Fixed orifice | TXV / EEV | Likely cause |
|---|---|---|---|
| Low superheat (<3–4 K) | Overcharge, low airflow, low indoor load | TXV overfeeding, bulb loose | Risk of liquid to compressor |
| Normal | Per charging chart (varies with conditions) | 5–10 K | — |
| High superheat | Undercharge, restriction, high load | Undercharge, restriction, TXV underfeeding | Starved coil, poor capacity |
Systems with a fixed orifice or capillary tube are charged to a target superheat that changes with indoor wet-bulb and outdoor dry-bulb temperature; always use the manufacturer's charging chart. TXV systems hold superheat roughly constant, so the charge is set by subcooling instead.
Pressure–temperature values here are interpolated from published PT charts; for blends such as R410A the dew-point value is used for superheat, as is standard practice. Gauge pressures assume sea-level atmospheric pressure.
Related products & guides
FAQs
What is normal superheat for R410A split AC?
On a TXV/EEV system, about 5–10 K at the outdoor unit. On fixed-orifice systems the target varies with conditions — typically 5–20 K — and must be read from the manufacturer's chart.
Why is my superheat very high?
The evaporator is starved: undercharge, a restriction (filter drier, kinked line, blocked capillary) or a metering device underfeeding. Check charge and pressures before adding refrigerant.
Can I use this calculator for R32?
Not yet — the PT data included covers R410A, R22 and R134a. Use the manufacturer's R32 PT chart.
Where should I measure suction temperature?
On the suction line within 10–15 cm of the service port, with the probe strapped tightly and insulated from ambient air.