Tools and setup
You will need a pressure reading, a line temperature reading, and the correct pressure temperature chart for the refrigerant. The best results come from taking both readings close to the same point in the system and comparing them with the right target for the job. If you want a simple overview first, start with the glossary or the PT chart.
Superheat steps
Measure suction pressure, convert that pressure to saturation temperature, then measure the suction line temperature at the same location. Subtract saturation temperature from the measured line temperature. The result is superheat. If you want a guided workflow, use the calculator or the main site for the app overview.
Subcooling steps
Measure liquid pressure, convert that pressure to saturation temperature, then measure the liquid line temperature. Subtract the measured liquid line temperature from the saturation temperature. The result is subcooling. Check the equipment target and compare your reading with the manufacturer’s guidance rather than using a one size fits all value.
Blends and glide
With blended refrigerants, the point you use depends on the task and the guidance you follow. For superheat, use the dew point. For subcooling, use the bubble point. If you are unsure, check the equipment documentation before you calculate.
Cheat sheet
Superheat is suction saturation temperature subtracted from suction line temperature. Subcooling is liquid line temperature subtracted from liquid saturation temperature. Keep the pressure and temperature readings paired, use the correct PT chart, and compare the result with the target for the specific system. For reminders, records, and a PDF report, see get the app.
Reference only. Verify with manufacturer data and gauges. Follow the manufacturer chart and EPA rules. This site is not an approval from EPA.