It appears to be a German version of what in the US is called a Humidistat. If you are leaving your home for a protracted time (say a vacation) and are concerned about mold and mildew that might build up if you shut down the A/C, this device will allow the A/C to come on only when the relative humidity rises above the set level. Otherwise, you set it at 0% and the A/C works normally.
Silent_Internet_4119 t1_j2b0cd3 wrote
Reply to Errmahgerd!! A HERRMIDIFIER!!! by paint_chips_kid
It appears to be a German version of what in the US is called a Humidistat. If you are leaving your home for a protracted time (say a vacation) and are concerned about mold and mildew that might build up if you shut down the A/C, this device will allow the A/C to come on only when the relative humidity rises above the set level. Otherwise, you set it at 0% and the A/C works normally.