Upgrade Honeywell Thermostat to Nest Learning

[Wocius]

I have a Trane Air Handler (Model TEM6A0D48H41SAA) with a Honeywell T6 Pro Programmable Thermostat (Model TH6220U2000/U) with the following 7 wires: C, G, Y, O/B, W2, E, R. 

It is an electric heating and cooling unit. I don’t know if it has a heat pump – although my online research suggests that the lack of a W wire may indicate that it does.

I am upgrading to a Nest Learning Thermostat (3rd gen.), and the Nest app suggests the following wiring: 

(1) C >C     (2) G>G     (3) Y >Y1     (4) O/B>O/B     (5) R>RH     (6) E>*     (7) W2>W1

My basic questions are:

• What is the significance of the original installation using a W2 wire and not using a W wire?  and
• Does the Nest-suggested configuration, especially moving the W1 wire to W2, look right?

This is a wonderfully useful forum. TIA for any and all help!

Wo

[listairee]

Hello @Wocius,

Thanks for reaching out. From your image, it looks like on some connector, it has 2 labels. Take your white wire for example, it is connected to a connector that is labeled as AUX and W2. The W or W1 wire usually controls your heating system while the W2 wire can control different types of heat based on the type of system you have. 

If you are unsure of your system, it is best to contact a local HVAC professional to help with this.

Hope that helps! 🙂

[Wocius]

Thanks for your fast reply!  Yes, the current configuration has the white wire going into W2/Aux, and the Nest app recommends putting that into W1.  I may have to contact a local Pro, but I'd like to try to DIM (Do It Myself), if possible!

[listairee]

Hello @Wocius,

If you are able to figure out your current system, I will be able to assist but without that information, it will be difficult to do so. 

A local Pro might be your best bet to ensure this is installed correctly. 🙂

[Wocius]

Thanks again.  I can now confirm I do have a heat pump.

I reset my Nest, following the instructions for a heat pump furnace. As far as I could understand, that meant moving the original W2 wire out of Nest's W1 and into Nest's W2/Aux.  When I turned the unit on, it showed:

and then:

I could not find any info re e78 at nest.com/e78.

Any additional help would be much appreciated!

[Jenelyn_O]

Hi there,

Thanks for the update. E78 code means your Nest Thermostat detects a wire in the W2 and OB (*OB) terminals but not in the Y1 (heat pump) terminal. Could you please try to reseat your Y1 wire? After that, restart your thermostat by going to Settings, Reset, and Restart. 

I appreciate your help, @listairee.

Regards,
Jenelyn

[Jenelyn_O]

Hi Wocius,

Checking in if you were able to try the troubleshooting steps above. Please let me know if that works. 

Thanks,
Jenelyn

[Jenelyn_O]

Hello there,

We haven't heard from you in a while so we'll be locking this thread if there is no update within 24 hours. If you need assistance or want to discuss topics, feel free to start a new thread.

Best,

Jenelyn