Subcooling Calculator
Enter high-side pressure and liquid-line temperature; the calculator returns subcooling and a charging note.
What subcooling tells you
Subcooling is how far the liquid refrigerant leaving the condenser has been cooled below its saturation (condensing) temperature at the measured high-side pressure. It confirms that a solid column of liquid, not vapour, is being fed to the metering device. On systems with a TXV or electronic expansion valve, subcooling is the primary indicator used to set the refrigerant charge — the manufacturer specifies a target (often 5–12 K) on the outdoor unit label or installation manual.
To measure it: read the liquid-line (high-side) pressure at the service port, convert to saturated condensing temperature for the refrigerant, measure the liquid-line temperature with a clamp thermometer at the same point, and subtract the line temperature from the saturated temperature.
| Subcooling | Interpretation |
|---|---|
| Low (<3 K) | Undercharged, leak, or condenser starved of refrigerant |
| On target (typically 5–12 K) | Charge correct for TXV systems |
| High (>15 K) | Overcharge, non-condensables (air) in the system, or restriction in the liquid line |
Use subcooling together with superheat: high subcooling with high superheat points to a liquid-line restriction; low subcooling with high superheat points to undercharge. Pressure–temperature data is interpolated from published PT charts; gauge pressures assume sea-level atmospheric pressure.
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FAQs
What subcooling should an R410A split AC have?
Most manufacturers specify roughly 5–12 K at the outdoor unit for TXV/EEV systems; use the value on the unit label or installation manual where available.
Can subcooling be used on fixed-orifice systems?
Superheat is the primary charging method for fixed-orifice systems; subcooling is a secondary check only.
Why is subcooling high after a repair?
Overcharging is the usual cause; air (non-condensables) left in the system after poor evacuation also raises head pressure and apparent subcooling.
Does ambient temperature affect subcooling?
Head pressure rises with ambient temperature, but the target subcooling stays roughly constant on TXV systems — which is why it is a reliable charging indicator in UAE summer conditions.
