Choose a Testo refrigeration manifold by the measurements, valve configuration, supported refrigerants and connected probes you actually need. A digital manifold reads system pressure and can calculate saturation-based parameters, but superheat and subcooling also require reliable pipe-temperature readings. A manifold alone cannot verify a complete refrigeration diagnosis.
Match the workflow to the instrument rather than the model number
A screenless 550i requires the Testo Smart App, whereas a 550s can display pressure-derived parameters on its own screen; the 570s prioritizes longer trend capture. Each still needs a temperature sensor at the right pipe location to calculate superheat or subcooling. Compare the manifold block, probe bundle and refrigerant compatibility before buying. For a model-specific guide to the screenless manifold and Smart App workflow, see testo 550i measurement guide.
Which measurements determine the choice?
For basic service, technicians may need high- and low-side pressure and corresponding saturation temperatures. Troubleshooting adds suction and liquid-line temperatures, superheat, subcooling, pressure trends and sometimes evacuation measurements. A four-way manifold offers additional hose and service routing compared with a two-way block; the appropriate choice depends on the task and safe work procedure. For a model-specific guide to four-way measurement and longer trend capture, see testo 570s trend-measurement guide.
| Task | Measurement or accessory | Selection consideration |
|---|---|---|
| Pressure checks | Compatible manifold pressure sensors | Pressure range and correct refrigerant selection |
| Superheat/subcooling | Pressure plus reliable pipe temperature | Correct clamp location and good pipe contact |
| Evacuation verification | Absolute-pressure vacuum probe | Micron gauge location and isolation procedure |
| Charging by weight | Refrigerant scale | Scale capacity and method required by the equipment manufacturer |
testo 550s versus testo 557s
The testo 550s uses a two-way valve block; the testo 557s uses a four-way valve block. Both support smart measurement workflows and compatible external temperature or vacuum probes, subject to the precise package and accessory configuration. Do not assume that every advertised probe is included in every kit.
Procedure for a meaningful comparison
- List the refrigerants and equipment types serviced. Confirm the manifold’s refrigerant data and pressure rating.
- List required tests: steady pressure, superheat/subcooling, leak testing, vacuum trend or charging.
- Check whether wired or Bluetooth temperature probes are already available and compatible with the candidate kit.
- Compare valve layout, hose configuration and the site’s approved service workflow.
- Check current calibration/support, app requirements and accessory availability before purchase.
Worked example: superheat uses two different measurements
Hypothetical: pressure and refrigerant selection yield an evaporating saturation temperature of 4 °C, while the suction-line clamp reads 11 °C. Superheat is 11 − 4 = 7 K, equivalent to a 12.6 °F temperature difference. This illustrates the calculation, not a universal target superheat. An incorrect refrigerant selection or poor clamp contact can make the value wrong. For a practical guide to combining pressure-derived saturation temperature with a clamp reading, see testo 549i superheat guide.
Do not choose by screen features alone
Recovery, pressure tests, charging, brazing and refrigerant circuit opening should follow manufacturer instructions and applicable refrigerant-handling regulations. For A2L and other flammable refrigerants, verify the rating and compatibility of the full equipment and service setup, not just the manifold’s product description.