installing NEST with heat pump including Dehumidifier

[Rigmaster]

Picked up a 2nd gen NEST thermostat and was looking at install instructions to install it in my house. I currently have an electric heat pump, apparently with a Dehumidifier. NEST help chat says I need to hire a NEST Pro installer since I have a dehumidifier, but I am confident enough in my abilities that with a little guidance, I can do this myself without causing any damage.

Seems like the big deal is that if your Dehumidifier is a two wire, you need to install a relay, but if it's one wire, you can simply install the "Dehum" wire from the old thermostat on to the "*" terminal on the Nest.

I have not yet gone to the actual HVAC unit to see if it looks like a one wire or two wire dehumidifier, just trying to see if anyone else has been thru this before, and can provide some peace of mind that this is not that complicated, and I should be OK doing it myself, or not.

Thanks!

Rig


ps- the existing thermostat has the following terminals (only listing those with wires attached, and the wire color to the right of the terminal label):


W/W1- White
Y/Y2- Yellow
G- Green
R- Red
Y1/W2- Black
O/W2- Orange

S2- Brown
S1- Brown
DHum- Purple
C- Blue

 

[Stuff]

Verify that you really have a dehumidifier. Some systems just have a dhum terminal that slows down the blower on the a/c trying to get more moisture out of the air.

Assume S1 and S2 go to an outdoor thermometer?

 

[Rigmaster]

Verify that you really have a dehumidifier. Some systems just have a dhum terminal that slows down the blower on the a/c trying to get more moisture out of the air.

Assume S1 and S2 go to an outdoor thermometer?

Thanks Stuff, I'll check the exact configuration of the system, hopefully tomorrow.

Not sure what S1 and S2 go to, the NEST instructions say if you have them, they are not used for the NEST. There's no outdoor temp display, and I'm not aware of an outdoor temp sensor anywhere. I'll see what I can find out about that as well.

 

[Rigmaster]

Pulled the cover off the housing of the inside unit, no evidence of an actual dehumidifier, so it must be just a fan control. Still not sure about the S1/S2 brown wires, they appear to go thru the wall to the outside unit, but it's too dark and cold right now for me to go poking around out there. I'll have to check it during daylight.

Edit: here's the pdf of the unit in question, the exact model is the FVBNF003. https://www.eheatcool.com/media/bryant-fv4b-air-handler-specs.pdf

 

[Stuff]

A real dehumidifier is another unit the size of your air handler. Those Bryant units such as yours have a DH terminal that slows the fan down to help dehumidify. It has reverse logic so if you don't use it you need to put a jumper back on the air handler's control board.

For the Nest you can put the DHum wire on the * terminal and tell it that it is to dehumidify with a/c, to dehumidify-remove power to *, and to run fan.

You other connections are fairly normal.

W/W1- White -> W1
Y/Y2- Yellow -> Y1
G- Green -> G
R- Red -> Rc
Y1/W2- Black -> W2
O/W2- Orange -> O/B

S2- Brown
S1- Brown
DHum- Purple -> *
C- Blue -> C