Aprilaire 550 solenoid to Nest v2 thermostat

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Old 11-26-16, 06:34 AM
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Lightbulb Aprilaire 550 solenoid to Nest v2 thermostat

I've read all the threads relating to wiring the AprilAire 550 to the Nest, but I'm not 100% sure any of them match my scenario (plus when I attempt to reply to them I'm told they are too old and I should start a fresh thread). I'm relatively handy but not as familiar with HVAC wiring and don't want to risk frying my Nest or humidifier solenoid by hooking it up incorrectly. I would appreciate the community's comments on my setup. I've also read the Nest Pro Installer guide but, again, just looking for validation my proposed wiring is right.

Existing setup with both a t-stat and humidistat:
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Proposed wiring setup with Nest:
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Here are some photos (not sure if they help or not): https://goo.gl/photos/qKCcmxixxgM46H2u5

Thank you in advance.
 
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Old 11-26-16, 10:41 AM
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Welcome to the forums.

Since you are using the Trane to run the stat.... it must also run the humidifier. If you thought the Trane couldn't supply enough 24v power to run the humidifier.... then you would have the nest operate a relay that switched the humidifier to the extra transformer.

The C connection shown in pink is optional. nest claims no C connection to stat is required but it seems they run more reliably with it.

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Old 11-26-16, 01:40 PM
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Thank you for the prompt reply.

So I don't need the transformer at all? The current system has it and guess I don't understand why they would have one if it wasn't needed.

Also, can I put two wires into the nest C terminal? It looks like you're indicating I should connect the C from the furnace to the C on the nest and run a C wire from the nest to the solenoid. Is that correct?

With this setup I assume the Humidifier solenoid valve would only open to let water in when the heat & fan are on, right? Or could it humidify the air with just the fan (and without heat)?

Thanks again!
 
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Old 11-26-16, 03:20 PM
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You probably had the transformer to run the humidistat which is no longer needed.
You can put two wires under one screw terminal.

You can program the nest for humidity with HEAT only..... my choice.... or
blower and humidity..... no heat required.
 
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Old 11-26-16, 08:01 PM
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Great. That makes sense and is very helpful. So is this an accurate new schematic (and the dotted blue line is optional, but recommended?) I have six wires running to the Nest location so should be good.

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Old 12-10-16, 07:01 AM
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Was this configuration able to work for you? I have an Aprilaire 560 and I'm having similar trouble wiring. Nest's docs indicate that this "two-wire" humidifier would require the relay- why is this not the case?

Thanks!
 
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Old 12-10-16, 03:21 PM
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Yes, the schematic I posted worked for me. No need for the transformer or a relay. I did use the C wire to both the solenoid and the nest.
 
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