Unveiling TESTO 552i Vacuum Gauge Failures and Shortcomings - What You Need to Know

In this video, I will show you how TESTO’s 552i vacuum gauge behaves in a refrigeration system. The vacuum sensor in this gauge is of the Pirani type, and Testo claims that it provides very accurate vacuum pressure readings.
However, this gauge has three major problems. I contacted TESTO and presented my inquiries with a video demonstrating my test results, but they could not reasonably convince me that this gauge is working properly. In this video, I will show you the results, and you can be the judge of my inquiries. I included the three problems below:
1. Vacuum pressure is consistently measured in absolute terms. In the Testo 570s, atmospheric pressure serves as an input for displaying low and high pressures in absolute form. However, it appears that atmospheric pressure is not factored into the measurement of vacuum pressure. Altering the atmospheric pressure appears to have no impact on vacuum pressure readings. Notably, Testo 570 and 552 gauges automatically measure atmospheric pressure, and vacuum readings commence from this pressure. Even dial-type vacuum gauges have to be compensated for atmospheric pressure.
2. Accurate measurement of vacuum pressure is crucial for diagnosing the presence of moisture in the system. The 552i registers vacuum pressure below 26 mbar, and beyond this point, no pressure readings are displayed. Given that water vapor pressure at 22°C is approximately 26 mbar, even if the 552i shows correct pressure below 26 mbar (which it does not), what happens if the ambient temperature is above 22°C and moisture is present? The gauge will show nothing, and one cannot recognize that there is a leak in the system or moisture is present.
3. The readings of this gauge, even below 26 mbar, are not correct. I tested this myself and compared it with the 552 old model with an absolute sensor, which works like a charm.
At first, I thought that my sensor was faulty and acquired another new sensor, but they both behaved exactly the same way. I even tested Testo’s 552 gauge with a Pirani sensor, which is physically similar to the old model. However, this gauge also behaved the same way. My conclusion is that the Pirani sensor is not suitable for use in a vacuum gauge in refrigeration systems.