Quick answer: To measure refrigerant superheat and subcooling with the testo 570s, combine pressure-derived saturation temperature with an actual pipe-temperature reading. Check whether the named instrument supplies both quantities or needs a separate clamp probe.
What makes the testo 570s different
The testo 570s is a four-way smart manifold built for longer measurements. Testo describes intelligent anomaly analysis in the Smart App, large memory, hybrid power and 0.25% full-scale pressure accuracy for the specified current model. For broader model selection, see the Testo digital refrigeration gauge guide.
Prepare and carry out the measurement
- Only a certified technician should attach gauges to a charged refrigerant circuit. Confirm refrigerant type, equipment state, hose ratings and the system procedure.
- Measure the relevant low-side and high-side pressures with the appropriate manifold or pressure probe, and select the exact refrigerant in the instrument/app.
- Attach suitable temperature clamps to correctly identified suction and liquid lines. Allow readings to stabilize under a documented operating condition.
- For superheat subtract suction saturation temperature from measured suction pipe temperature. For subcooling subtract measured liquid-line temperature from condensing saturation temperature. Document dew/bubble conventions for blends.
Model-specific use and interpretation
Pair pressure/temperature inputs, choose the refrigerant and plan the logging interval, battery arrangement and operating mode. Record when defrost, staging or fan control changes occur while capturing superheat/subcooling trends. For a comparable instrument, see the testo 550i superheat guide.
Superheat = suction-pipe temperature − evaporating saturation temperature. Subcooling = condensing saturation temperature − liquid-line temperature. These are differences in K or °F, not percentages. The correct target depends on equipment design, metering device and test conditions; never use one universal charging target.
A time series distinguishes a repeatable operating pattern from one isolated reading; it cannot identify a particular refrigerant fault by itself.
Worked example (hypothetical)
Hypothetical 570s data: a stable 8 K superheat during steady operation rises to 13 K during a control transition and returns to 8 K afterward. Trend timing suggests investigating control logic and load changes before concluding that charge drifted.
Interpretation and common errors
- Unexpected readings can be caused by unstable load, low airflow, incorrect probe placement, poor clamp contact, wrong refrigerant, or a sensor that has not paired.
- A high or low value does not identify refrigerant charge on its own. Expansion-device type, manufacturer charts and control strategy matter.
- Do not charge, recover or open the system based solely on this article. Refrigerant work carries pressure, electrical and potentially flammability hazards and is for qualified personnel.
Use long-term logging rather than a spot-only diagnosis
The 570s is especially useful when a refrigeration problem appears intermittently. Record sensor assignments, refrigerant, logger start/end time, control events and battery arrangement so temperature and pressure trends can be aligned. The Smart App’s anomaly tools support investigation; they do not independently identify a failed expansion valve. For a slow cycling fault, a trend across multiple cycles carries more evidence than one attractive superheat figure. For guidance on choosing the logging interval, see the data-logging sampling interval guide.
Interpretation: If a pressure spike coincides with a valve-change event, investigate the control sequence before assuming contamination or undercharge.
Limits and safety
Follow the exact instrument manual and the equipment manufacturer’s acceptance criteria. The example is not field evidence, a legal limit or a commissioning target. Work on energized electrical equipment, combustion systems, charged refrigerant circuits or hot surfaces requires qualified personnel and the site’s approved protective procedures.