To perform a superheat reading for a refrigerant charge, take the pressure reading, and convert it to temperature using a charging conversion chart. Take the temperature of the suction line, and subtract this value from the pressure reading.
Turn off the air-conditioning unit before taking any measurements. Attach the gauge manifold hose to the pressure port, and turn the unit on. Let the unit run for 10-15 minutes. Then, use the metering device to take the pressure reading.
A charging conversion charge is usually provided by the manufacturer. Refer to this chart, and convert the pressure reading to temperature.Take an accurate reading of the temperature by using a thermometer to measure the suction line; a digital thermometer is ideal. Be sure to insulate the thermometer’s probe to stop surrounding air flow from impacting the reading. Compare the two values; the difference between the two readings is the superheat reading.
The superheat reading signals how much refrigerant is moving into the evaporator. The superheat reading can be lowered by adding refrigerant to the unit. Drain refrigerant to increase the superheat. A superheat reading that is too high means refrigeration energy is being wasted. A reading that is too low is a possible indication of excess liquid and compression damage.