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Nest Thermostat 3rd Gen + Aprilaire 224 Wiring

KoG506's Avatar

Join Date: Feb 2018
Posts: 2

02-08-18, 09:34 PM   #1 (permalink)  
Nest Thermostat 3rd Gen + Aprilaire 224 Wiring

Hi, I just placed an order for a Nest thermostat to replace my old non-smart thermostat and Manual HUM stat. I did some researching but I cannot find the solution to the current HUM wiring to connect to the Nest when it arrives. I will provide as much details as I can.

Here's a diagram of the current manual-HUM wiring:

This is the Electronic Relay (ER):

In the service manual of my HUM Aprilaire 224 I found this diagram of what the ER is attached to. Also, this diagram wiring does NOT match with what the current wiring diagram above (weird) that I followed.

At the humidistat, there are two wires connected to it, RED and WHITE wire. When I turn the knob on the humidistat I hear a click-sound(CS) and another CS when I turn it backwards. The CS is always heard whether the furnace is running or not. BUT I do also hear a CS coming somewhere from the furnace (I assume its the ER) when the furnace is running.

So my first question is, how do I connect to the Nest (*) with the two RED and WHITE wire from the Humidistat?

2nd question, can I just connect the unused BLUE wire thats coiled around the HVAC wiring to the HVAC "C" on motherboard to have it active? I want to connect the C wire to the nest. The current HVAC wiring to the Thermostat is not using a "C" wire.

Current HVAC wire to the Non-smart thermostat:

Here's a video of the HVAC wiring too: (Video is still processing as of 11:33 PM EST, but its available for download)


Thank You!!

Last edited by KoG506; 02-08-18 at 09:37 PM. Reason: Picture
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KoG506's Avatar

Join Date: Feb 2018
Posts: 2

02-09-18, 11:08 PM   #2 (permalink)  
Disregard, it has been solved.

PJmax's Avatar
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Join Date: Oct 2012
Posts: 41,205

02-09-18, 11:16 PM   #3 (permalink)  
Very good. I was waiting for pictures.

~ Pete ~

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