Refrigeration guide
Superheat vs Subcooling
Both are temperature differences from saturation, but they describe different refrigerant states and must be measured at stated locations.
The direct distinction
Superheat describes vapor warmer than its matched saturation temperature. Subcooling describes liquid cooler than its matched condensing saturation temperature. Neither number alone is a universal charge setting, because the refrigerant, equipment, measurement point, and manufacturer procedure matter.
Formulas and locations
| Check | Formula | Typical boundary |
|---|---|---|
| Superheat | Measured suction-line temperature − matched saturation temperature | Evaporator outlet or compressor inlet; state which one |
| Subcooling | Matched condensing saturation temperature − liquid-line temperature | Condenser outlet or expansion-valve inlet; state which one |
Worked example
A 40°F matched evaporating saturation temperature and 50°F suction-line measurement produce 10°F superheat (5.56 K). A 100°F matched condensing saturation temperature and 90°F liquid-line measurement produce 10°F subcooling. The arithmetic is simple; matching refrigerant data and locations is the critical part.
Use in HVAC/R work
These values help describe refrigerant state at an identified boundary. A technician may use them within the manufacturer’s specified procedure, while a designer may use them as documented operating assumptions. They do not replace pressure-temperature data, equipment instructions, or a complete diagnosis.
Common mistakes
- Using a pressure-temperature value for the wrong refrigerant or blend convention.
- Comparing an evaporator-outlet saturation value with a compressor-inlet temperature without stating line effects.
- Treating a negative calculated difference as a target rather than rechecking the inputs and locations.
- Applying a generic target from another system.
Related tools
- Refrigerant Superheat Calculator
- Refrigerant Subcooling Calculator
- Refrigeration Units and Measurement Reference
Sources and scope
This guide explains measurement differences only. Use the manufacturer procedure and appropriate refrigerant property data for service decisions.