Nest compatibility with water based heat pump?

[GaryG4]

I have a pan early generation Nest working for years on our high rise condo water based heat pump system and want to install newer third generation thermostat. The current install does not have black wire utilized, should I do same wiring as current thermostat? Current is Y1, G, Rc, OB, and black wire is not plugged in. Thanks!

[EduardoN]

Hi @GaryG4,

Thank you for contacting this community! I understand that you've had a Nest Learning Thermostat (1st gen) for years, and it's been working with your condo's heat pump. Now you're thinking about upgrading to a newer model, the Nest Learning Thermostat (3rd gen), and I'm happy to help you with that!
To give you the most accurate information, I'd like to ask you a few questions:

• Could you send me a picture of the wires connected to your thermostat?
• Could you send me a picture of the wires connected to the control board of your HVAC system?
• What is the make and model of your HVAC system?

Please feel free to share any additional details you think might be relevant.

Best regards,
Eduardo

[GaryG4]

Hello - and thank you!

I tried to copy/paste photo but says I don’t have permission to upload photos?

the make of the HVAC equipment is Trane. It’s a water based heat pump system, single zone, single stage, heat and cooling.

five wires at t-stat are yellow, green, red, white, and black wire that’s not currently used on 2nd generation Nest -T-Stat. 

[EduardoN]

Hi @GaryG4,

Thank you for the update and for all the information you've shared. Regarding the wire compatibility, I want to confirm that the wires connected to your original Nest Learning Thermostat should be connected in the exact same way to the Nest Learning Thermostat (3rd gen).

To provide you with more information on compatibility, I'd like to ask you a couple of questions:

• Which terminal was the black wire connected to on your previous Nest Learning Thermostat?
• Is your system for heating only, cooling only, or both?

Keep me posted.

Best regards,
Eduardo

[GaryG4]

The black wire is not currently connected on existing Nest thermostat. HVAC is both heating and cooling - water source heat pump.