Wiring compatibility

[molecularvision]

I have a train thermostat that is on its last leg, and I would like to replace it with a nest thermostat. However, I’m not quite sure whether the nest system is compatible. S1 and S2 I can tape off and ignore. Most of the rest of the wires look like a perfect match, but I am having severe trouble with how to process the white wires I have.  The white wire goes into X2, But there is a jumper between that line and W1. I have no idea even where to begin. Has anyone run across this? 

[zoeuvre]

Hi molecularvision, 

Thanks for posting here in the Community forum and for showing interest in our Nest Thermostats. Fortunately, your thermostat wires are compatible with our Nest Learning Thermostat 3rd generation and should be wired to the Nest Learning Thermostat as shown:

Take note that S1 and S2 are not needed for Nes Thermostats; these wires can be indicator lights or sensor wires. The Nest thermostat uses its LCD display instead of an indicator light and gets sensor information, like outdoor weather conditions, over Wi-Fi. The X2 terminal of your Trane thermostat is for emergency heat, so it should be connected to the * terminal of the Nest Learning Thermostat. Also, here's a guide for the installation and setup of a Nest Learning Thermostat.

Let us know if you have any other questions.

Best,

Zoe 

[molecularvision]

Zoe,

thank you very much for this information and I have purchased a nest thermostat you recommended. Can you tell me a bit more about what I do for the white wire that is labeled into the asterisk/star?  What should I prescribe this to be in the app during set up?  is there an option to say emergency heat?  Again, thank you very much, and I am happy to be a new customer!

[Jenelyn_O]

Hi there molecularvision,

Chiming in — that's a good question. Your white wire (X2) might be your emergency heat or auxiliary heat. To ensure, could you please provide the make and model of your heat pump system? 

I appreciate the help, Zoe.

Thanks,

Jenelyn

[molecularvision]

I have a trane XR, model 4twr4024d1000aa.  I think it might be an XR14, but I’m not entirely sure. If it helps, with the old thermostat, I do not see an auxiliary heat setting, but there is an EM heat setting.  The thing that confuses me is the short between the X2 and W1, but if all I need is emergency heat, that’s fine with me.

[Jenelyn_O]

Hey molecularvision,

Thanks for providing your heat pump system make and model. You can configure your white wire as your emergency heat. Also, no worries about the small wire that jumps between your X2 and W1, just don't use that wire, as the Nest Thermostats don't use jumper wires. 

Please let us know if you still have questions in mind, as we'll be willing to help.

Cheers,

Jenelyn