Aprilaire Humidifier Controller getting Cooked

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Old 12-05-14, 09:09 AM
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Aprilaire Humidifier Controller getting Cooked

I installed a Aprilaire 500 humidifier with a model 60 digital controller, onto my DMO (Olson) BCL-120S oil furnace. Burner uses a Honeywell R8184G ignition module.

When the furnace turns on, humidifier controller wakes up and reads humidity level. When the blower kicks on, the solenoid on the humidifier opens and water begins to flow as it should. All good so far. But when the burner shuts off and the blower motor is left running on its own, one of the capacitors on the 60 controller circuit board burns up. I now have a new controller hooked up but the symptoms are still the same. I can feel the capacitor heating up, so I immediately shut the system down before any harm can be done.

I believe I can see why this is happening. I removed wires one at a time from the controller to see which was causing the capacitor to heat up. It was the white wire that goes to the W terminal on the furnace. I measured the voltage between the C and W terminals on the furnace and get about 26VAC with the burner on and also with the burner and blower on together. But when the burner shuts off, leaving just the blower running, it jumps to 54VAC. I believe this voltage is damaging the humidifier controller.

Is this voltage normal? If so I need to find an alternative way to wire up my humidifier. I think I would possibly need to use a voltage sensing relay.
 
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Old 12-05-14, 09:28 AM
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I've only worked on one system like that. The humidifier was connected to a terminal marked ACC, I assume for accessories. If you disconnect the humidifier completely, do the over heating still occur?
 
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Old 12-05-14, 11:39 AM
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Good guess on the voltage sensing relay. The following is how I wire that humidifier to an oil furnace.

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Old 12-06-14, 02:10 PM
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Thanks PJmax. I'll go that route. Thanks for the wiring diagram. Because "how to wire it?" would have been my next question.
 
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Old 12-11-14, 06:05 PM
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Well I bought a Aprilaire A50 24V relay but I don't think it is working correctly. Before I wired it up, I tested it with my meter and it shows continuity across the leads. Shouldn't this be a "normally open" relay? I did install it just to see if maybe I was missing something. It passed the 24V through without the furnace even running as I suspected it would.
 
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Old 12-11-14, 06:37 PM
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It's a current sensing relay that uses a bit of the 24vac going thru it to activate it.

Try something..... temporarily
Connect the R and W wires together. That will turn the humidistat on.
Put the A50 in one of the H black wires so that it is in the humidifier loop.

Let me know if the solenoid operates. It shouldn't until the A50 senses current flow.
 
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Old 12-14-14, 06:47 AM
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I wired relay in line with the solenoid and it does not open. Ran blower common wire through relay and solenoid opens when blower is running. So I guess the relay checks out ok. Only issue with this configuration is that the humidistat is powered up all the time. Still can't figure out why relay isn't working when inline with the white wire. Both transformers are putting out about 26V
 
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