Quick answer: The testo 552i participates in system evacuation, but its role must be identified correctly: the 552i is the vacuum sensor, while the 565i is a pump that can use a 552i to control an automated evacuation and hold test.
What makes the testo 552i different
The testo 552i is a wireless absolute-pressure micron gauge, not a refrigeration manifold or vacuum pump. Its official measuring range extends to 20,000 microns, with accuracy specified only under defined conditions. For related guidance, see 565i: How to Run a Refrigeration Vacuum and Hold.
Prepare and carry out the measurement
- Recover/reclaim refrigerant as required and perform the approved integrity test before evacuation. Refrigeration work is for qualified personnel.
- Connect a suitable evacuation setup and position the micron sensor on the isolated system side—not only at the pump inlet.
- Start the pump or approved automation using the equipment maker’s target, observe pressure fall and log sensor position and elapsed time.
- Isolate the pump as directed; observe absolute-pressure rise over the prescribed period and investigate moisture, trapped volume, leaks or measurement placement before deciding the system is ready.
Model-specific use and interpretation
Fit the probe at a suitable system service port on the system side of isolation; connect via Bluetooth to the Smart App or compatible Testo manifold. Monitor the evacuation trend, then isolate the pump and observe the documented holding period.
Microns describe absolute pressure. A pump running for a long time can coexist with a misleadingly low reading if the sensor is isolated behind a restriction. A decay slope is an investigation tool, not a leak-vs-moisture diagnosis by itself.
Micron readings from a gauge near the pump may differ from those at the system; a falling number is not proof that a system is dry or leak-free.
Worked example (hypothetical)
Hypothetical vacuum trend: 1,200 microns before isolation, 850 microns after additional pumping and 1,450 microns five minutes after isolation. The rise is 600 microns, but the pass/fail decision must use the equipment maker’s test duration, threshold and conditions.
Practical interpretation
Place the gauge where it reflects system vacuum rather than solely the pump inlet. A low pump-side reading can coexist with inadequate evacuation elsewhere due to restrictions. For a broader checklist when evacuation is unusually slow, see why pulling a vacuum takes longer.
A pressure-rise trend after pump isolation can result from leaks, moisture evaporation, outgassing or a disturbed connection. The shape of the trend helps guide testing but is not a unique fingerprint. For the causes and test implications of this pattern, see why vacuum rises after pump isolation.
Illustrative example: a system reads 420 microns at pump isolation and 640 microns ten minutes later. The rise is 220 microns over ten minutes (22 microns/min average). This is a trend calculation, not a pass/fail diagnosis. Moisture vaporization, leakage, trapped refrigerant and gauge/hose behavior can all contribute; refer to the system-specific criterion.
Keep the micron gauge on the system side
The 552i can be installed at a service port with its angled connection and can transmit absolute-pressure readings to the Smart App or supported manifolds. A reading near the pump may not represent the system because hoses have finite conductance and valves may restrict flow. Place the gauge at a representative system port, record isolation timing, and follow a specified decay test rather than one arbitrary micron threshold.
Interpretation: A 500-micron pump-inlet reading alongside a 1,800-micron system-port reading would show that instrument location, rather than pump performance alone, needs investigation.
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.