ICESQUARE / Troubleshooting
What subcooling is and how to measure it
Subcooling is the number of degrees a liquid is below its saturation temperature. It helps assess whether the refrigerant has enough margin to reach the expansion valve as liquid.
- Saturation 40 °C
- Minus liquid reading 34 °C
- Subcooling 6 K
Measure at a representative location
Stabilize the equipment and measure liquid-line temperature with pressure at the same location. A pressure reading from farther away may skew the calculation if there is pressure drop. Use the location specified by the manufacturer.
Subtract in the right order
Convert pressure to saturation temperature. For blends with glide, use the bubble point. Subtract actual liquid temperature from saturation temperature. For example, 40 °C minus 34 °C gives 6 K of subcooling.
Use it as part of the diagnosis
Read it alongside superheat, pressure drop through filters and the liquid line, heat exchanger condition and receiver configuration. In transcritical CO₂ operation above critical pressure at the gas cooler outlet, there is no saturation temperature. Use the parameters specified by the equipment controls.
Guide for trained technicians. Follow the manufacturer’s procedure and limits for the refrigerant and equipment model being serviced.
Technical references
- Danfoss · Dimensioning of Refrigeration Components, Part 2 · “Thermostatic Expansion Valves”
- Danfoss · Ref Tools, Refrigerant Slider · “Dew and Bubble Point”
- Danfoss · Troubleshoot Cold Room Faults · Diagnosis Guide
- Danfoss · Industrial Refrigeration Application Handbook · “Transcritical CO₂”