Connect Nest to Honeywell DR90 Dehumidifier


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Old 08-23-14, 12:11 AM
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Connect Nest to Honeywell DR90 Dehumidifier

Thanks in advance for any help. Just bought a Nest thermostat. I would like it to control my dehumidifier as well. It is a stand alone with it own supply and return ducts so it functions independently of the HVAC system. I simply want it to turn on and off depending on the humidity set point. It is currently wired to a humidistat. It seems like it would be easy but I know Nest has one port for a wire but the current humidistat has 4 wires between it and the unit. Any help pointing me in the right direction would be greatly appreciated.

Chris
 
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Old 08-23-14, 05:19 AM
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Welcome to the forums.

Since the dehumidifier is a stand alone device you would need a 24vac relay to interface the two together. The current heating/cooling system would run the nest on its 24vac transformer and the nest would activate the dehumidifier which also has its own transformer.
 
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Old 08-23-14, 09:54 PM
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Thanks for the reply. I am still slightly confused. I apologize for being a NOOB. So on the Dehumidifier, there are 4 contacts. One labeled Dehum, C, R, and Fan. The C and the R terminals both put out 24Vac. If I jump the R terminal to the terminal labeled Dehu it energized the dehumidifier fan and the coils which is what i want. So my question is how to get the 24Vac to the terminal labeled Dehu. I thought the * wire from the nest would deliver that volage to it? Is that not correct? Does the R terminal then need to be grounded? Or should I connect the R and the Dehu terminals to a relay and then one wire to the nest so that the nest closes the relay when it calls for dehumification? If that works I don't understand why the wire directly to the Dehu terminal doesn't work.
Sorry for my limited understanding if wiring. Hope my question makes sense. As a side note, the dehumidifier is in a different room than the HVAC so I can't use any power terminals from there meaning I need to use one of the powered terminals on the Dehumidifier.
 
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Old 08-23-14, 10:38 PM
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I would like it to control my dehumidifier as well.
That means you want the nest to control two items. The furnace and the dehumidifier. Each one has its own internal 24vac transformer and they cannot be combined or used in a combined method. The relay is used to separate the 24vac control voltage from the humidifier.

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Old 08-24-14, 01:52 AM
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Thank you very much PJ! That diagram helps me understand. Just to clarify, the C wire running out of the relay goes to the Nest, correct? Can I put it in the same slot as the C wire that currently comes from the HVAC unit? Also, is that a common relay I can get at Home Depot etc.? Thanks again. I really appreciate it.
 
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Old 08-24-14, 09:44 AM
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You can have more than one wire on the C terminal.

You can use any normally open 24vac relay. In the link below is a typical one that I use a lot of. I don't know if depot carries a similar part.

24vac HVAC relay at Amazon
 
 

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