| Refrigerant | Pressure (psig) | Estimated Saturation (°F) | Liquid Temp (°F) | Subcooling (°F) |
|---|---|---|---|---|
| R-410A | 400 | 95 | 85 | 10 |
| R-22 | 200 | 81 | 70 | 11 |
| R-134a | 150 | 84 | 76 | 8 |
| R-404A | 300 | 77 | 66 | 11 |
| R-407C | 350 | 87 | 78 | 9 |
Subcooling is the drop in temperature below the liquid saturation temperature at the same pressure.
- Subcooling (°F) = Saturation Temp (°F) − Liquid Line Temp (°F)
- Subcooling (°C) = Subcooling (°F) × 5/9
When you choose the pressure method, the calculator converts your condenser pressure to a saturation temperature using a simplified pressure–temperature chart and linear interpolation between points.
- Select the refrigerant used by the system.
- Choose your method: enter condenser pressure, or enter saturation temperature directly.
- Measure the liquid line temperature near the condenser outlet and enter it with units.
- Optionally set a target subcooling and tolerance to get a quick assessment label.
- Press Calculate Subcooling to view results, then export CSV or PDF if needed.
1) What subcooling represents
Subcooling is the difference between the liquid saturation temperature (at measured condenser pressure) and the measured liquid-line temperature. Positive subcooling confirms a solid column of liquid at the metering device, improving stable feeding and predictable capacity.
2) Typical field targets
Many comfort systems with a TXV are commonly commissioned around 8–12 °F of subcooling, while fixed-orifice systems are often charged by superheat. Manufacturer data is the final authority because coil design, refrigerant, and line set details change the optimum.
3) Where to measure
Record liquid temperature on the liquid line near the condenser outlet, ideally on clean copper with good thermal contact and insulation over the sensor. Take pressure at the liquid service port. Let the system stabilize 10–15 minutes after adjustments before logging readings.
4) How pressure becomes temperature
The calculator estimates saturation temperature by converting gauge pressure to a saturation point using an interpolated pressure–temperature chart for the selected refrigerant. Interpolation fills the gap between table points, producing a practical estimate for quick field decisions.
5) Interpreting low subcooling
Low subcooling (for example, below 3 °F) can indicate undercharge, insufficient condenser airflow, high outdoor load, or measurement error. Low subcooling may allow flash gas in the liquid line, which can cause erratic feeding and reduced performance.
6) Interpreting high subcooling
High subcooling (often above 18 °F) may point to overcharge or liquid-line restrictions such as a partially plugged filter-drier, kinked line, or closed service valve. Restrictions raise the condensing pressure and can create abnormal temperature splits across components.
7) Common accuracy pitfalls
Clamp sensors need insulation and stable contact; a bare clamp can read several degrees high or low. Pressure errors come from hose losses, wrong port selection, or mislabeled units. Always confirm refrigerant type, stabilize operating conditions, and recheck after each charge change.
8) Reporting and documentation
For commissioning, record refrigerant, ambient conditions, liquid pressure, saturation temperature, liquid temperature, and calculated subcooling. Saving a CSV supports trend comparisons across visits, while a PDF report is useful for handover documentation and warranty discussions.
1) What is a good subcooling number?
A common starting point for many TXV comfort systems is 8–12 °F, but the correct value is the manufacturer’s target for that specific model, refrigerant, and operating condition.
2) Can I charge a fixed-orifice system by subcooling?
It’s possible in some cases, but fixed-orifice systems are typically charged by superheat. Use the method specified by the equipment documentation and charging chart for best results.
3) Why do I get negative subcooling?
Negative subcooling suggests the liquid line is at or above saturation, meaning flashing may be occurring. Verify sensor placement, insulation, steady operation, and that the selected refrigerant matches the system.
4) Does outdoor temperature affect subcooling?
Yes. Outdoor air and condenser cleanliness affect condensing pressure, which changes saturation temperature. Stabilize conditions, confirm airflow, and use manufacturer charts that account for ambient conditions when available.
5) Where should I clamp the temperature sensor?
Clamp on the liquid line near the condenser outlet on clean metal, then insulate over the sensor. Avoid spots influenced by heat sources, direct sun, or contact with other tubing.
6) What if my gauge already shows saturation temperature?
Select the direct saturation method and enter the displayed saturation temperature. Then enter the measured liquid-line temperature to compute subcooling without relying on the simplified chart interpolation.
7) How much should I adjust charge if I’m off target?
Adjustments depend on system size and conditions. Make small changes, allow time to stabilize, and re-measure. If readings are inconsistent, resolve airflow or restriction issues before adding refrigerant.