Subcooling equals saturation temperature from liquid line pressure minus actual liquid line temperature, measured at the outdoor unit. It shows how much liquid is stacked up in the condenser and makes sure solid liquid reaches the metering device. TXV systems are charged to the manufacturer's target subcooling, commonly around 8 to 12 degrees F; low subcooling points to undercharge, high to overcharge or a restriction.
TXV system, so I'm charging to subcooling, target is 10 and we're at 4, add a little and let it settle.
Subcooling tells you about the condenser and charge; superheat tells you about the evaporator. Read both before adding anything.
Also heard as
- SC
- liquid subcooling
Related terms
Superheat
How many degrees refrigerant vapor is above its boiling point at the pressure it is at.
Saturation
The state where liquid and vapor refrigerant coexist, so its temperature is locked to its pressure.
TXV
Thermostatic expansion valve: a metering device that adjusts refrigerant flow to hold constant evaporator superheat.
Flash gas
Liquid refrigerant that turns to vapor because its pressure dropped, either at the metering device or where it shouldn't.
Weigh in
To charge a system with a measured weight of refrigerant on a scale, set by nameplate charge and line set length.