Aprilaire Humidistat - Not Tripping Solenoid


Old 12-04-05, 10:14 AM
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Aprilaire Humidistat - Not Tripping Solenoid

I have an Aprilaire 440 bypass humidistat controlled by an Aprilaire 56 automatic humidistat. The humidistat is wired to my furnace heat terminals (white/common) and is confirmed to be getting 24VAC.

My problem is that the humidistat is not tripping the humidifier water valve solenoid, even in test mode. Specifically, the humidistat is outputting about 20VAC to the solenoid and the solenoid is receiving about 0.1A but does not switch on. This amperage is lower than I would expect, but having replaced both the humidistat and the solenoid valve with no change in condition, I'm not sure what to do next.

Thanks in advance for any assistance in this matter.


Chip Zaenglein
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Old 12-04-05, 06:57 PM
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Location: Rochester, Minnesota
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20 volts is not enough to open the valve..

I do not suggest stealing power from the t-stat to power this humidfier system.. You must use another transfomer.

Read STEP 10 in your install manual.
Old 12-10-05, 07:51 AM
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Thanks for the help. I'll get the transformer.

Chip Zaenglein
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