Nest compatibility

[lateralus]

Hello - I'm trying to determine if my wiring/system is compatible with the Nest and the compatibility checker seems inconclusive. I would insert a picture but I don't see a way to do that here. The wires are as follows: W, Y, G, R, B. There is a C slot but nothing is attached to it. Thanks in advance for any assistance. 

[Patrick_Caezza]

You can post a picture by clicking on the picture icon in the reply widow. 

[CoolingWizard]

@lateralus , if your old thermostat has both a B terminal and a C terminal, then your old thermostat is capable of supporting a heat pump. Do you know if you have a heat pump?

AC Cooling Wizard

[lateralus]

[CoolingWizard]

@lateralus , it does look like you possibly have a heat pump because I noticed that the blue wire is connected also to the Y wire at your air handler. Can you get me another picture of your air handler from the left side of that control board so I can see better the wires are connected to which terminal on that air handler control board? 

AC Cooling Wizard

[lateralus]

As requested, I'm attaching a few pics of the left side in hopes you can see what you need to see. Thx!

[Patrick_Caezza]

@lateralus 

Based on the Control PCB picture that you supplied I would say to have a conventional system and not a Heat Pump.

I don't see the blue wire connected anywhere on the control PCB so it doesn't appear to be needed at the thermostat. You can verify this by looking at the thermostat cable that is connected to the Control PCB and you'll proboly see the blue wire handing loose or cut of where the wires exist the cable covering.

I also see that there is only a white and a yellow wire connected to the Y terminal and when you follow the white wire back to the cable there will be a red wire that is connected to the C terminal and goes to the outdoor unit.

With all of this in mind you can just move the wires from your current thermostat to the Nest thermostat by matching the terminal labels.

You can also add the Blue wire to the C terminal on the Control PCB and the C terminal at the thermostat.

Besure to power the system off at the breaker before doing anything.

[lateralus]

@Patrick_Caezza Thanks for your thoughtful response. Can I safely assume that connecting the Nest will not cause some sort of "bad" event if it ends up that it is not compatible? Thx!

[Patrick_Caezza · Accepted solution]

@lateralus 

I would confidently say you don't have a heat pump based on the pictures you have provided and my experience.

You only have two wires going to the outdoor unit. If you had a heat pump you would have more that two wires.

I suggest you wire the Nest like this

White - W to W

Yellow - Y to Y

Green - G to G

Red - R to R (jumper not needed)

Blue - leave disconnected until you verify that the Nest is working and the connect to the C terminal at the thermostat and to the terminal block on the control PCB.

[lateralus]

@Patrick_Caezza Hi again. I have done as you have described but am getting a "no power to Rc" on the Nest. A few items of note: (1) there are two red wires going into the PCB - one to the R terminal, the other to the C terminal, which now has a red and blue wire going to it. I tried moving the 2nd red wire up to the R terminal with the other red wire, but this had no effect. (2) The wire going into the W terminal on the PCB is more of a tan color, with the actual white wire going into the Y/ terminal. This is how it was when I first started the "project" so it seemed to be working fine before, but just thought I'd mention it.

[lateralus]

Update: I think I am good now. The doors/panels to the furnace were not all the way closed and apparently there is a trigger or sensor that was keeping something from working. Thanks for your help - much appreciated!

[Patrick_Caezza]

@lateralus 

Yup, that will bite you every time.

There are several safety interlocks with the cover being one. There is also an interlock on the drain that will trigger if the drain is clogged.

[lateralus]

Thx for the replies. As to whether or not I have a heat pump ... I don't know. How would I know this? 

Thanks again.

[CoolingWizard]

@lateralus , do you have access to the outdoor unit? There is a manufacturer label. It’s on the outside of the unit and if you can get me a model number, I can double check to see what type of system you have.  

AC Cooling Wizard

[lateralus]

Please see image of outdoor unit label.