Nest with AprilAire Dehumidifier & Furnace


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Old 09-03-23, 11:24 AM
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Nest with AprilAire Dehumidifier & Furnace

I have a furnace and a dehumidifier I'd like to tie together on the Nest thermostat. I could use some advice on the setup. The dehumidifier is setup with its own independent fan.

I've attached the current wiring setup.

Note: The HVAC installer said I had to purchase a different thermostat to hook them together, whereas the manufacturer of the dehumidifier said it would work with Nest. I'm also not sure if the HVAC installer connected the 2-stage correctly (i.e. the W1 & W2 wires). Picked up a C-wire adapter just in case (was $1).

AprilAire 1850 control board to Dehumidifier Control (Model 76)
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Daikin Two-Stage Furnace (Model DM96VE) with Multi-Speed ECM connecting to Nest Thermostat (as setup by installer).
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Vent setup that I'm wondering if the installer set it up correctly.
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Picked this C wire Adapter thinking it may be useful?
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What are your thoughts on all of this?
 

Last edited by DarkAbyss; 09-03-23 at 01:00 PM.
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Old 09-03-23, 11:30 AM
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Hello.

I'm currently out on the road but will check for you as soon as I get back to my shop.

I can tell you that you will need a SPNO 24vac relay as the dehumidifier requires a contact closure to operate and the nest can't supply that on 1 wire.
 
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Old 09-03-23, 01:11 PM
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Interesting, they told me it wouldn't work with the Nest and I needed to buy a new Thermostat.

Also the furnace drain pipe was installed below the float switch on the Little Giant Condensate Pump (554401).


Little Giant 554401 (No safety switch)

Apparently there was a lot of rust in there when they did maintenance and the next day the condensate pump wouldn't work. FYI: On their invoice, it said they checked the drain. I put an air pump on it and blew out a lot of debris on both ends.
 
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Old 09-03-23, 04:25 PM
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Old 09-03-23, 11:12 PM
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You would need a wire on W1 and W2 between the furnace and the nest.
That would be for the nest to control the two stages.
The way it's set up now second stage is probably timed based on running time via W1.

I can make up a wiring diagram based on the relay you choose.
The 90-290q is fine.
Basically the coil side of the relay connects to furnace C and the * terminal on the nest.
The N.O. switch contacts connect to DH on the dehumidifier.
When 24v is sent out on the * .... the relay closes and brings on the dehumidifier.
You no longer would need the humidistat.

 
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Old 09-04-23, 06:35 PM
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Am I warm?I think I'm off on the Dehumidifier hookup.
 

Last edited by PJmax; 09-05-23 at 02:06 PM. Reason: modified diagram
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Old 09-05-23, 02:07 PM
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Close.
 
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Old 09-10-23, 04:10 PM
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Please let me know the proper way. I should be getting the switch this upcoming week.
 
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Old 09-10-23, 04:44 PM
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I modified your drawing. It shows modified at the bottom of the page.
 
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Old 09-11-23, 09:44 AM
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It goes to the DH! Doh!! I wouldn't have guessed that.....I was thinking a common wire had to go to the Nest.


P.S.

Thank you!!!!
 

Last edited by DarkAbyss; 09-11-23 at 10:36 AM.
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Old 09-11-23, 03:38 PM
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I wired it up and for some reason Nest thinks I have a cooling unit. Not sure why that is.


 
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Old 09-11-23, 03:45 PM
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You have to relearn the thermostat. During that relearn you tell it what the * function is.
 
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Old 09-11-23, 04:05 PM
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One issue is the furnace fan is constantly on. I set the * to standalone dehumidifier in pro mode.
 
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Old 09-11-23, 04:35 PM
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In Pro setup.... right after you click on the * you should see this screen.
You need to deactivate the fan.
 
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Old 09-11-23, 05:40 PM
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Deactivated the fan. No change.
Did a factory reset on the Nest, then re-setup. No change.
Checked the wires on the Nest and Furnace.Y to Y1, W1 to W1, R to RH, G to G....Furnace Common (C) to switch then Switch 1 to * (Nest)... They're correct. Can the switch to thermostat be reversed? The Humidistat proprietary controller was disconnected along with the wires.

Nest Pro Settings:
Y1:
Type: Conv. cooling
Source: Electric
Delivery: Forced Air

W1:
Conv. Heating
Source: Gas
Delivery: Forced air
Fan: Activate

*
Type: Dehum Standalone
Fan: Don't active

RH:
Power

G:
Fan

Could W1 Fan be the issue?
 
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Old 09-11-23, 05:58 PM
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A gas furnace should be don't activate. The furnace controls the fan.
 
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Old 09-11-23, 06:42 PM
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Done....No change.
Though it is interesting the thermostat has a low battery and can't connect to the internet to run tests.
The dehumidifier works fine.
 
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Old 09-12-23, 06:11 AM
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Last night the Nest thermostat didn't turn on the Furnace and the Nest battery died due to lack of power.
Plugged the Nest into a USB charger this morning.
With the fully charged thermostat the heat works along with the dehumidifier. I'm waiting to see if the fan will turn off.

 
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Old 09-12-23, 12:22 PM
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Contacted Dehumidifier support:
"our dehumidifiers use a 2-wire dry contact connection to the third-party thermostat. The diagram you provided looks correct in reference to the dehumidifiers DH DH terminals going to an isolation relay so the thermostat can convert itís 24V signal into a dry contact."

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Current status

Battery: 3.660 V
Voc: 35.66
Vin: 6.67 V
lin: 20 mA(i)


Looked up the info:
3.7 V is required to install a software update

Voc: should be 29 to 42 V
Vin: should be 29 to 42 V
Lin: should be 200 to 385 mA

https://support.google.com/googlenes...zippy=%2Cpower

The forums stated a lot of weirdness happens when you don't get full power.

I redid the diagram to make it look nicer too.


 
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Old 09-12-23, 01:13 PM
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Based on research on Nest thermostat's and this setup, it looks like an AC Adapter (24 Vol Transformer) hooked up to the thermostat RC and C wire might solve the issue.
 
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Old 09-12-23, 09:07 PM
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Try moving the red R wire to Rc instead of Rh on the nest first.
Rc is the terminal that power is referenced to.

Do you have any other spare wires between the stat and furnace ?
If you do... connect C of stat to C of furnace.
 
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Old 09-14-23, 05:22 PM
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Smile

Moved the Nest red R wire to Rc instead of Rh. No change.
Didn't see any extra wires.

Added AC Adapter to RC and C wire. Nest thermostat with dead battery came on and is charging.

Status when I plugged it in (thermostat)
Battery: 3.414 V
Voc: 36.86
Vin: 36.86 V
lin: 200 mA(c)

It works!!! Thank you!!!
 
 

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