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Subcooling = saturation temperature (from high-side pressure) − actual liquid line temperature. It tells you how much the liquid refrigerant has been cooled below its condensing temperature, helping ensure solid liquid to the metering device.
Why it matters: • Proper subcooling supports stable metering device operation (especially TXV systems) • Low subcooling can mean undercharge or condenser not filling with liquid • High subcooling can mean overcharge or restriction (context matters)
Worked example (calculation): High-side pressure corresponds to Tsat 110°F. Liquid line temp = 98°F. Subcooling = 110 − 98 = 12°F.
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