The noise reduction system has two components, one that attenuates differential noise (between live and neutral) and one that attenuates common mode noise (between live/neutral & earth).
Differential noise reduction (differential noise is noise between live & neutral) remains active even without earth reference.
If there is no earth/ground reference (two red LEDs) there is no “reference” for the common mode noise reduction circuit.
It also means the system operates without mains earth, which in many cases will place the user at the risk of electric shock, including potentially lethal shocks. Note that that is unrelated to the AC iPurifier, it merely indicates this problem, it does not cause it.
Without an earth/ground reference, the common mode noise reduction circuit is inoperative (common mode noise is noise that exists between the Earth and the two power conductors, Live & Neutral). An earth/ground reference may be provided via the earth/ground terminal on the unit, however, this does not replace the safety earth function (though the red LED should turn off).
Common mode noise is generally produced by all switched-mode power supplies in varying degrees and is the largest problem. It may be possible to achieve substantial noise reduction by adding an earth-wire from the earth port on top of the AC iPurifier to the case of the largest noise-producing device (usually the one with the highest power consumption).
A better choice is to add a true earth to the system, from earth rods driven directly into the soil (traditional houses) or to approximate one in concrete-floored buildings with steel reinforced structures by placing a large metal plate (> 1m^2) on the floor (below tatami/carpet) directly on the concrete.
Short Answer:
The differential noise reduction remains active even without earth reference, however, the common-mode noise circuit will be inoperative.
