What subcooling means
After vapor condenses to liquid, additional heat removal lowers liquid temperature below saturation.
That difference is subcooling.
How it is measured
High-side pressure is converted to saturation temperature and the liquid-line temperature is subtracted.
Probe placement and stable operation matter.
Low subcooling
Low subcooling may indicate low charge or insufficient liquid in the condenser.
It should be interpreted with superheat and load.
High subcooling
High subcooling may indicate overcharge, a restriction, or refrigerant stacking.
A restricted TXV can create high subcooling and a starved evaporator.
Charging by subcooling
Many TXV systems specify a target subcooling value.
Airflow and coil condition should be verified before adjustment.
Frequently asked questions
Is there one correct number?
No.
Does high always mean overcharge?
No.
Can a dirty condenser affect it?
Yes.
Why does a TXV need it?
It needs a dependable liquid column.
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