Nest Learning... cool and emergency heat ok, but not regular (heat pump) heat.

[awolf21]

I have a heat pump system with electrical backup heat (no gas furnace).
Spoke to Nest before installing a learning thermostat.
They told me:
Yellow to Y1
Brown to Y2
Green to G
Orange to OB
Red to Rc
White to W1   <----
Blue to C
Black to *   <----
Cooling works fine. No heat.
Without changing wires, I fooled with settings on the thermostat, and I now have emergency heat.
But no "regular" (heat pump) heat.
Wondering if the wiring is wrong.
I see a lot of confusion online about the two wires I bolded above (White, Black). Should white go to W2?
Suggestions?

[CoolingWizard]

@awolf21 , if you can post the picture you took of the wiring on your old thermostat I know I can help straighten this out. 
With a heat pump you must put auxiliary heat in W2.  The OB wire is what changes the mode from cool to heat and back. 
since you have a Y one and a Y2, this tells me that you also have a two-stage compressor on your heat pump. 

if my answer helped you to understand your problem better how about hitting the Kudo button down below? If my answer helps solve your problem why not tap Recommend this Answer below.

AC Cooling Wizard

[awolf21]

No permission to upload images, so I put it on ImgBB...

https://ibb.co/S0Gv787

If hard to make out colors, I can post those in text.

Thank you!

[awolf21]

It is hard to make out...
On left, top to bottom...
brown
black
white

On right, top to bottom...
red
orange
yellow
green
blue

[CoolingWizard]

@awolf21 

All thermostats manufactured are colorblind. It is sad but it is true. Your old thermostat has:

RED on Rc with jumper wire to R

GREEN on G

YELLOW on Y

BLUE on B

BROWN on Y2

BLACK on X2

WHITE on W1

On the Nest Learning Thermostat your wires will be:

RED to Nest RC

ORANGE to OB

YELLOW to Y1

GREEN to G

BLUE to C

BROWN to Y2

WHITE to W2

BLACK not used

AC Cooling Wizard 

[CoolingWizard · Accepted solution]

@awolf21 

You have a bit of a unique situation. The X2 wire is from the outdoor unit. In the winter time, when the outdoor unit goes into defrost mode, it uses the BK wire to signal the thermostat to turn on the auxiliary heat. While in defrost, therefore you don’t get cold air coming back into the house. Some manufacturer simply turned the blower off During defrost. Some manufactures like train for example turn on the auxiliary heat.   
When we install systems like this, we do not rely upon the thermostat to activate auxiliary heat, we wire the BK wire at the air handler to auxiliary heat. On your thermostat when the system was set up, the BK wire is automatically linked to the W1 terminal your auxiliary heat is actually on W1. Place white wire on W2 of your Nest Learning Thermostat .  The black wire on X2 needs to be taped off.  
Now comes the hard part, there needs to be a wire jumper in your air handler control board that connects X2 to W2 auxiliary heat. Sometimes the air handler has the word AUX But most often is simply W2. 

If my answer helped you to understand your situation or problem, hit the kudos thumb down below. If my response actually solved your problem then please Recommend this Answer to others. 

AC Cooling Wizard

[awolf21]

Thank you much!
Haven't done this yet but will report back if issues.

[awolf21]

Hi. Went into Trane air handler. In the Coil unit I found the controller board...
https://ibb.co/QH3TbLC
Closeup photo of connections...
https://ibb.co/THqVYdF

There's a W2, with two wires in it.
But no X2.
Is it BK or some other connection?

------------- 

Related question... I have 4 completely separate systems in my house.
I may put Nest thermostats on all 4. 
On one of the 4, access to the controller board in a TINY attic crawl space will require a small monkey.
I'd like a monkey, but don't have one.
What bad consequence(s) for that one if...
I do make the thermostat wiring change (white wire on W2) but do not try to put a jumper on the controller board? As best I understand this (poorly) some cold air coming into the house briefly during our non-existent central Texas "winters." If that's all, I might give this a pass... 

[AxelD]

Hi awolf21,

Thanks for posting in the community! Sorry to hear that after the installation, it's not heating up. I understand that wiring issues with your Nest thermostat can be frustrating. To ensure the problem is addressed correctly and safely, I recommend contacting an HVAC technician or Nest Pro. They have the expertise to diagnose and resolve wiring issues specific to your heating and cooling system.

Regards,
Axel.