Refrigeration
Superheat and Subcooling Field Notes
A charging reference for deciding which number matters, what the pattern suggests, and when airflow must be solved first.
How to read the pair
- Look at superheat and subcooling together instead of treating one number like a verdict.
- Use stable indoor and outdoor conditions before calling a charge final.
- Verify condenser cleanliness and fan performance before chasing impossible charging numbers.
Pattern guide
| Pattern | Possible direction | Next check |
|---|---|---|
| High superheat, low subcooling | Often undercharge or starved evaporator | Leak search, airflow, metering device |
| Low superheat, high subcooling | Possible overcharge or liquid stacking | Weigh-in history, condenser airflow, line restrictions |
| Low superheat, low subcooling | Overfeeding TXV or compressor issue | Bulb placement, compressor performance |
Charge after these checks
- Filter, coil, blower wheel, and fan speed are clean and reasonable.
- Indoor load is real enough to stabilize the evaporator.
- Condenser coil is clean, outdoor fan is healthy, and line-set restrictions are not obvious.