What superheat means
Once refrigerant has fully boiled into vapor, additional heat raises its temperature above saturation.
That temperature difference is superheat.
How it is measured
Suction pressure is converted to saturation temperature and subtracted from measured suction-line temperature.
Correct refrigerant selection and stable conditions are essential.
High superheat
High superheat can indicate low charge, a restriction, underfeeding TXV, or high load.
It does not prove low refrigerant.
Low superheat
Low superheat can indicate overfeeding, low airflow, low load, or liquid refrigerant leaving the evaporator.
Very low superheat can threaten the compressor.
How technicians use it
Fixed-orifice systems may use target superheat for charging.
TXV systems are often charged by subcooling while superheat is monitored.
Frequently asked questions
Is there one correct number?
No.
Does high always mean low charge?
No.
Can airflow change it?
Yes.
Is it used on heat pumps?
Yes.
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