Wire Aprilaire 700 (Automatic) to RUUD Furnance

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Old 11-17-12, 09:00 PM
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Wire Aprilaire 700 (Automatic) to RUUD Furnance

I'm in the process of connecting an Aprilaire 700 (Automatic) unit to a RUUD Furnace. It's a RUUD UGRA Achiever 90 Plus, with circuit board:

Model Number: 1028-928A
Part Number: 62-24140-04

The wiring diagram for the Aprilaire 700 is as follows:



The circuit board looks like the following:



Three questions:

1) The furnace circuit board has a HUM contact on the bottom near the center, marked as a Humidifier Relay. What exactly is the purpose of it? Can it supply the continuous 24 VAC power the Aprilaire diagram requires? Should I ignore this relay when installing this humidifier?

2) The Humidistat control panel (the digital panel that comes with the humidifier), interrupts the thermostat's blower signal. According to the diagram, you connect the G wire from the thermostat to G on the humidistat, then Gf from the humidistat to the G on the furnace. Shouldn't these wires be run in parallel to the furnace instead in serial? The only purpose I could discern is if the humidifier wanted to disable the fan signal from the thermostat, but I can't think of a scenario where this would make sense.

3) The Humidifier unit has two brown wires coming out of it, which appear to be unmarked. Does it matter which is wired to the humistat and which is wired to the 24 VAC transformer, or are they interchangeable?
 
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Old 11-18-12, 07:08 AM
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1-Can you take a photo of your wire diagram on the blower door?? We need ot know if the HUM is 120v or 24v.

2-Skip the G/Gf hook up.. I find that running the fan to add humidity doesn't do much good.. It runs a lot of water vs having it run with the heat only.

3-The two wires are interchangeable.
 
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Old 11-18-12, 08:54 AM
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1) For the HUM contact, the circuit board was replaced and the original didn't have a HUM relay so I would need to use a meter to know for sure. I understand that if it's 24V I can wire directly to the humidifier and if it's 120V I can attach the 24 VAC transformer. Either way, though, does this relay only fire when the circuit board tells it to or is it continuously powered?

4) If the HUM relay fires only when told to, it means I can decide whether the circuit board should control the Aprilaire Humidifier or the Humidistat digital panel. The Humidistat has access to two sensors the circuit board does not: an outdoor temp sensor and a return air temp sensor. Also, the Humidstat can fire with no heat (since I'm connecting the humidifier to hot water) and in the summer if humidity is low. That said, is it better to have the furnace circuit board making those decisions?

Thanks in advance!
 
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Old 11-19-12, 06:48 AM
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Correct,you'll need a meter to find out what the board is putting out on this.

With the Aprilaire, the way I'd wire it to only come on with heat (ignoring the G and Gf hook up), the HUM will be wired for the humidifier solidnoid valve. There is no need to add humidity in the summer at all.
 
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Old 11-19-12, 04:56 PM
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Update: Finished installation over the weekend and it works perfectly. I ended up going with the Aprilaire fully automatic instructions including wiring the G/Gf in serial. I also ignored the HUM relay on my circuit board since the Humidistat has two extra sensors that help it determine when the humidifier should be ON, that the circuit board does not.

The humidifier is connected to hot water so it can run with just the blower or in the summer. As far as only wanting the humidifier to run when the heat is on, that can still be achieved just by using the digital humidistat panel:

1) The digital panel contains a switch to disable blower activation so the humidifier can be set to only turn on when the furnace is activated

2) If I don't want it to run in the summer, I just turn the dial to "off". My thermostat requires manual intervention to switch between COOL and HEAT (like most thermostats) so when I go to turn the AC on in the summer, I can disable if need be.

Thanks for the help everyone!
 
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