New Nest Thermostat blows only cold air

[PhilHF]

I have two  heat pump units which were controlled by Honeywell thermostats. Two years ago I replaced  one of the Honeywells with a Nest learning thermostat, which still works ok. I just installed a new Nest Learning thermostat on the other system. Despite following install instructions it now only blows cold air regardless of whether it is set to heat or cool. Tried resetting and reinstalling but problem remained. Out of curiosity I compared the wiring connections with what I had on my other ac and noticed that on that older unit the red wire was connected  to Rc terminal whereas I had the new one connected to RH.  I then turned the new system off and changed the red wire  to the Rc terminal.  This did not work as it still blew cold. I then replaced it with the Honeywell I had taken out and everything worked as before.

As an experiment I reset the new Nest to factory default and swapped it out with my other system only to find the same problem as on the new installation. Common sense would suggest that the new Nest is faulty. As I bought this from SRP, our electric supplier I will return it over a refund  but noticed on their website that although returns are accepted, I will have to pay shipping so was wondering if their is any point in contacting Google and requesting a no charge swap for a working unit.

[Markjosephp]

Hello PhilHF,

It seems like you've done a thorough troubleshooting process with your Nest Learning Thermostat installations. It's frustrating to encounter issues despite following the instructions diligently. Your observation about the wiring differences between the two systems is interesting, but it's unfortunate that the adjustment didn't resolve the problem.

Considering the Nest Thermostat worked on the older system and exhibited the same issue when swapped to the new one, it does raise concerns about the unit itself. I'd love to know more about this.

• Have you had a chance to change its orientation? You can find the steps in troubleshooting heat pump issues article.
• Can you post a picture of your old thermostat and Nest Thermostat's wiring setup?
• Gather the power readings in the Technical Info settings.
• Look for any wiring reports, message codes, or check for undetected wires in the Equipment settings.

Keep me posted.

Regards,
Mark