The Hermetic Moisture Indicator works by utilizing a unique salt that holds more water than a traditional green/yellow indicator salt. This salt also changes through a wider color range than the green/yellow salt. Additionally, the indicator itself is thicker, and together these attributes allow for a wide range of rich colors that enhance the ability to better understand the amount of water in the refrigerant. In addition, the HMI, along with all other moisture indicators, does not simply sense parts per million (ppm) of water in a system. Instead, it measures relative humidity. This is a significant distinction. Why? Because, for example, a reading of 50 ppm in R12 is extremely dangerous, while 50 ppm in R-410A is not. The difference is in the refrigerants. The new refrigerants, along with their POE oils, can physically hold more water; and since they operate at low ppms, this translates into extremely low relative humidity levels, in the 2% to 7% RH range.
There is a misconception across the HVACR industry that 10% RH moisture detection is sufficient. That’s an assumption that can lead to a dangerous — and expensive — false sense of security. At 3% RH in many HFCs, a green/yellow indicator will show a green color, pronouncing the system is still “dry.” In fact, it is actually at risk of acid formation from the breakdown of the POE oil. At 10% RH moisture detection, the system has already been contaminated with moisture and acids, and will need to be cleaned. That could mean anything from replacing the filter-drier and exchanging some or all of the oil in the system, to replacing a compressor or multiple compressors. Actually, the old green/yellow indicators show a “dry” reading as high as 7% RH. And a 7% RH reading in R-410A means there are nearly 300 ppm of water present. Emerson Climate Technologies’ studies have shown that acid begins forming at approximately 75 ppm, when water starts to turn POE oils back into acid. That means the newer refrigerants, with their high moisture content, see severe problems to the lubricant at 100 ppm. Any acid formation can be a problem, of course. So detecting moisture content as soon as possible is crucial to protecting the life of the system. Again, traditional green/yellow indicators fall short. By the time the indicator goes off, damage is already occurring to the lubricant. So it’s an indication that doesn’t actually indicate anything.