Aprilaire 700 fan not working

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  #1  
Old 01-11-19, 08:08 PM
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Aprilaire 700 fan not working

We moved into a house that had an Aprilaire 700 with a manual humidistat installed. It had been working fine, but the other day I noticed the humidity in the house had dropped about 10%. After some experimentation I determined that the fan is not running anymore.

When the furnace is running and I turn up the humidistat, the soloniod engages, water flows into the panel, but the fan does not running. The power for the fan is connected to an outlet on the side of the furnace. I traced the cables back into the furnace and the outlet is wired with the ground to the metal holding the control board and the hot wire to a terminal on the board labeled HUM.

After I cycled the power to the furnace the first time it ran it sounded like the fan was trying to start up, but didnít. On subsequent runs, the water turns on, but it doesnít even sound like the fan tries to start. Iím trying to determine how to test further.

Does the HUM terminal supply a constant voltage or only when the fan is supposed to run? Can I try plugging the power cord into a wall outlet? I plugged a usb charger with a LED into the outlet wired into the HUM just to see if it was providing power and it didnít come on even when the soloniod engaged.

Thanks in advance for suggestions for next steps.
 
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  #2  
Old 01-11-19, 08:23 PM
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HUM terminal is normally active (120v) only when the furnace is actively heating. The humidifier fan neutral normally connects to the neutral terminals on the board. Going to the chassis is not right.
 
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Old 01-11-19, 08:31 PM
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Welcome to the forums.

The 700 gets plugged in and has it's own internal transformer. When the brown wires are shorted..... the yellow solenoid wires become live at 24vAC and the fan runs. If the solenoid is opening..... the problem is the internal fan.

Also..... that white/neutral connection to ground is wrong. There are spare neutral connections on the board.
 
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Old 01-11-19, 09:00 PM
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Thanks for the quick replies. The wire connected to the chassis looks like bare copper, so I assumed it was ground and not a neutral. Maybe there is a separate neutral wire I missed, it was hard to tell since the wires were bundled. Iíll double check.

If the HUM terminal is putting out a normal 120v, I would have thought the usb LED I plugged in would have lit up when the furnace ran. If I want to verify it is the fan, can I plug the unit into a wall outlet and short the two pins on the connector where the brown wires would go? If the fan doesnt run then, based on what youíve said it would definitely be bad.
 
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Old 01-12-19, 12:11 AM
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can I plug the unit into a wall outlet and short the two pins on the connector where the brown wires would go?
Yes...... you can do that.
 
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Old 01-12-19, 08:07 PM
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I got an extension cord and plugged the unit into a wall outlet. The fan now runs when the water engages.

The water engages (when heat runs and humidistat trips) whether the unit is plugged in or not. Iím confused on this since I thought the power to open the soloniod was coming from the board which needed to be plugged in.

Given how the outlet wired into the furnace control board is setup Iím not clear how it was ever working.
 
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Old 01-12-19, 08:15 PM
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You need to be using the HUM output to power the humidifier. You said you tested the HUM output and it was dead. It will only turn on when the furnace is in heating mode..... burner firing.


Let's take a quick step back. There are two 700 humidifiers. Old style and new. With the old almond colored case style..... you needed to short the two brown wires to get the fan to operate and the solenoid open. This model needs the 120 HUM.

With the newer gray case style..... the two brown wires need 24vAC connected to them to make the fan work and the solenoid open. You need to verify which one you have.
 
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Old 01-13-19, 06:40 AM
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First, thank you for all the help. Unless the HUM output died recently, I'm thinking this must have not been working properly previously and the drop in humidity in the house might be from external weather (had between 35 to 40% RH, but now is between 25-30%).

I have attached some photos and will do my best to describe the overall setup as I can tell. The humidifier is gray in color (see Humidifier Outside.jpg). It has a normal grounded power cable that runs into the back of the cover (the warning label on the cable says 120V). The system has a manual control on the return that lets you set the humidity between 15 to 45% (Manual Control.jpg).

The two brown wires in the humidifier are capped to a red and white wire coming out of the side of the HVAC (brown wires.jpg). Inside the humidifier, the brown wires go into two of the pins in a four pin plastic connector (yellow wires.jpg). The other two pins in that connector have yellow wires which are capped to longer yellow wires that run to the water control solenoid. The other side of the plastic connector is on the cover (part with the fan), and it connects when the cover is closed. The wires from the connector on the cover go back behind the fan.

The observed behavior of the system:
  • If the furnace is not running, adjusting the humidity control does nothing (as expected)
  • If the furnace is running, when I turn the humidity control up, I hear a click and the water starts running into the panel.
    • This happens whether the black 3 prong power cord is plugged in or not.
  • Plugging the black 3 prong power cord into the outlet on the furnace has no effect. Whether it's plugged in or not, the water will turn on, but the fan does not run.
  • When the black 3 prong power cord is plugged into a wall outlet, the fan runs when the water is running (furnace running and humidity control turned up). It stops running when the water stops, but the fan blades will spin for a little while while once the motor stops.

I have found the user manual (how to operate it), but no installation manual on how it should be wired up. The furnace control board appears to have been replaced in 2015 and has part number S9230F1014 / 100870-03. I have the installation instructions for the board.
 
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Last edited by JAHMD; 01-13-19 at 06:47 AM. Reason: clarifying something
  #9  
Old 01-13-19, 10:34 AM
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You have the newer model that requires 24vAC on the control leads for operation. The 24vAC goes directly to the solenoid which is working as you've told us. That means the furnace wiring is correct. It also goes to a relay to activate the fan. The 120v plug needs to be connected to an always live receptacle for the fan to work.
 
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Old 01-13-19, 05:04 PM
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Thanks for your help. It sounds like an extension cord to a wall outlet will work for now.

The outlet wired into the HUM terminal clearly isnít working properly, but even if it was it sounds like I should not be using it. Maybe it was there from a previous install.
 
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