Calculating Superheat
Superheat is the temperature increase of refrigerant vapor above its saturation (boiling) temperature at a given pressure. To calculate: read the suction pressure with your gauges, look up the saturation temperature on a PT chart, then measure the actual suction line temperature with a thermometer. Superheat = Actual Suction Temperature minus Saturation Temperature. Example: R-22 suction pressure is 68 psig, which corresponds to 40°F saturation on the PT chart. If the actual suction line temperature reads 50°F, then superheat = 50°F - 40°F = 10°F.
Superheat = Actual Suction Temp - Saturation Temp. Example: 50°F actual - 40°F saturation = 10°F superheat.
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