Trane 16 xli heat pump X2 wire should go to W2 AUX or * Emergency?

[yoyo11]

Hello, I am replacing a Trane Thermostat for Trane 16 xli heat pump system with Nest Learning Thermostat (4th Gen). I seem to have figured out most of the wiring but I am confused regarding X2. Nest has not label/notion for X2. As per forums and other searches, X2 on Trane mean emergency heat. On Nest the equivalent is * (Emergency).

Question:

1. Is Auxiliary heat the same Emergency Heat? I don't think so
2. Where should X2 wire go on the Nest? I am of the opinion it should go to * (Emergency) an not the W2 Aux
3. Where should W1 wire go on the Nest? I am of the opinion it should go to W1. Some suggest it should go to W2 Aux
4. Trane thermostat also as wires goint to S1 and S2. From what I can tell they are for outdoor sensor. Nest Learning Thermostat doesn't care about S1 and S2. Thus I should leave them open (apply electric tap to both).

@Patrick_Caezza  can you help with the Nest Learning Thermostat wiring? I have attached the Trane Thermostat wiring diagram, Thanks.

[Patrick_Caezza]

@yoyo11 

To answer your questions

1. Auxiliary heat and Emergency heat are the same except Emergency heat is manually selected when needed.
2. You are correct, it goes to the * terminal and you set it to emergency heat.
3. You connect W1 to W2/AUX and set it as AUX heat.
4. Again, you are correct. Just tape them off.

Give this wiring a try,

Brown - Y2 to Y2

Black - X2 to * (set as emergency heat)

White - W1 to W2/AUX (set as AUX heat)

White - S1 - Tape off

Red - S2 - Tape off

Red - R to Rc (jumper to RC not needed)

Orange - O to OB

Yellow - Y to Y1

Green - G to G

Blue - B to C

[yoyo11]

@Patrick_Caezza, thanks a lot for the detailed response. Appreciate it.

I wired as per our discussion and your response. The Nest Learning Thermostat did turn and prompt me through setup (though it took a while, as it kept saying attach to base, thermostat powering down). Once it was up and running, once the temp dropped  (almost 5 degrees) below the preset value the thermostat still didn't turn on the heat. During the testing everything seemed to work fine. I decided to revert back to hold thermostat. Also on the Nest App, when I selected the wiring, it says thermostat not compatible. I am thinking to go with another compatible brand for Trane XL 16i. Thanks again for your detailed response. Appreciate it.