I have a aprial air 400a. I have aready checked resistance from oat. It is fine. I have 24v at solenoid valve until I connect the leads to the actual valve. Then I loose voltage. The way I have it wire Is with a constant 24 volt to r and c at the humidisat. A constant circuit from w on on furnace to the h term at humidistat then from the w term at fur to to solenoid. the other side of h term at hum stat also geos to the other side of the solenoid.. I know the solenoid is fine cause if I wire a direct 24v to the valve it come on with no problems. I cant find a wiring diagram anywhere for this particle model
Humidifiers - Aprilaire - 400 Humidifier
Answers & Comments
I don't really have a "solution" but you might want to check the resivoirs for lime/calcium buildup as they can defeat the signal by the sensors thinking that the system is full of water. Some vinegar and a toothbrush resolves this. The other possibility is that your sensors may be deflected below (not in contact with) the resivor bottom.