Faulty Aprilaire humidifier - help


Old 09-10-04, 01:03 PM
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Question Faulty Aprilaire humidifier - help

There is an Aprilaire 440 humidifier in our new home with a manual humidistat mounted on the family room wall. Water is dripping non-stop to the water panel, even when the humidistat is set to OFF (and the blower is off).

I suspect the humidistat is faulty, since I got zapped when I touched an exposed wire connected to the solenoid valve with the humidistat set to OFF. I assume there should be no current to the valve when it is set to off and it should be controlled by the humidistat. Am I right?

Does anyone have a wiring instruction for the humidistat?

The house is 14 years old. Should I replace the whole thing or just replace either the faulty humidistat or the faulty solenoid valve ?

Old 09-13-04, 01:15 PM
Ed Imeduc's Avatar
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The house is 14 years old. Should I replace the whole thing or just replace either the faulty humidistat or the faulty solenoid valve ?
Dont know how old it is ? But 14 years Id get a new one for sure. If you are on AC turn the water off to it on the water line.

Old 09-16-04, 02:22 PM
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i agree with ed, 14 years is a good life for a humidifier.

as to the wiring, that is a bypass type, so the only real part is the solenoid valve, which is replaceable.

here is how it works.....

24 volts is supplied from either a dedicated transformer or the transformer in the furnace. this should run to a "model 50" sensing relay that is attached to the heat fan speed, closing the circuit when amperage is sensed through the fan wire. it then travels to the humidistat that closes on call for humidity, then to the solenoid valve energizing and opening it. the voltage then proceeds back to the common side of the transformer, completing the circuit.
many do not use the "model 50" and get the 24 volts from W, which is energized on call for heat. the problem with this is that the humidifier will start right away on call for heat instead of waiting for fan to come on.
some units have HUM terminals on the circuit board, depending on brand. even then, you have to check the voltage, as some are 24 volts output on these terminals, and some 115. the 115 terminals i wire to power an independant transformer, only powered on heat call plus fan, eliminating the "model 50" relay

unwire one of the wires going to the solenoid, if it quits, the problem is electrical, (probably humidistat) if it continues to run, solenoid is stuck open, see that all the time too, usually caused by build up from water supply

with all of that being said, the only real parts are the solenoid and media inside the unit, the rest being case, distributor tray etc.

i would fix it and save a good bit

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