Thermostat Gen4 upgrade from Gen2 Heat pump problem

[RobC18]

I have been happily using the Gen2 thermostat with my heat pump.

I have installed the Gen4 with exactly the same wiring and settings.  The cooling mode works correctly.  When the heat mode is selected, the heat pump runs in the cooling mode through a full cycle before it finally switches to heat and then runs OK.  This seems to be occurring because it turns on the heat pump before it switches the reversing valves.  The O/B is selected for B and switches Cyclically.  

[EduardoN]

Hi @RobC18,

Thanks for contacting this community! I understand that you upgraded your Nest Learning Thermostat (2nd gen) to a 4th gen model. Your old thermostat worked perfectly, but with the new one, when you turn on the heat mode for a short period, the cooling mode turns on first, and then the heat mode works correctly. No worries, I'm here to help!

To provide the most accurate information, I'd like to ask you some questions.

• Which wires do you have installed on your new thermostat? If you can send me a photo that'll be easier.
• What type of furnace do you have? (gas, electric, etc.)
• How long does the cooling run before it changes to heating?
• When was the last maintenance check for your HVAC system?

In this situation, you have indicated that the O/B is selected for B. However, let's try selecting O on your Nest Learning Thermostat in the following way:

• On your thermostat, go to Settings.
• Select Equipment.
• Select Continue > Continue.
• Select Heat Pump.
• You have selected B let's select O.

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

Best regards,
Eduardo

[RobC18]

Thanks for responding Eduardo.  

I have a 2 zone system using a ZoneFirst H32 zone controller.  This has been working great with 2 Gen2 thermostats for over a year for both heating and cooling.  The Gen2 thermostat still works correctly, but the Gen4 does not work the same.  When the Gen4 calls for heat, the zones work correctly, but a cooling cycle starts.  This runs for almost 10 minutes, then a fan only purge, and then the reversing valve is activated.  The status LED on the H32 indicates this correctly and the correct zones are enabled.  

Wires connected: G,Y1,OB,Rc,C

I live in Southern California, so there is no need for a secondary heating source other than the heat pump.  The system is an ACPRO.

Any guidance would be appreciated.

Thanks,

Rob

[RobC18]

The 10 minutes seemed like a longer time than I remembered.  I left the thermostats off for a while and redid the timing.

When the mode is HEAT and the gen4 calls for heat, it runs for 2 minutes cooling the house.  It then does its fan purge for about 2 minutes and then switches the reversing valve and starts heating.  The gen2 switches the reversing valve as soon as heat is called for.

[EduardoN]

Hi @RobC18, 

Thank you so much for keeping me updated on everything, including the photo of the connected wires. Regarding what you mentioned about having a two-zone system, I'd like to verify the following information about your HVAC system:

• Could you send me a photo of your system's control board where the wires for your two zones are connected?
• Also, could you send me more information about your HVAC system (e.g., model, type)?

Keep me posted.

Best regards,
Eduardo

[RobC18]

Eduardo,

Here is my status at the moment.  Going through all the settings to answer your questions was a good review for me.  To get the gen2 to work, I had to set the set the reversing valve to cyclical and everything worked fine.  Whenever a cycle started on the gen4, it started in cool.  When I switched it to seasonal, it still started the heat cycle on cool. 

I then forced it to do a second heat cycle without an intervening cool and since the RV was already set, there is no issue!!  It should be good to go.  

I will install the second gen4 in the next day or so.

Let's put this discussion on hold unless the second unit has a problem.

Thank you for your interest and patience in this matter.

Best,

Rob

[EduardoN]

Hi @RobC18,

Thank you very much for keeping me informed about everything you've been doing with your system to get your thermostat working correctly. I understand you were going to install the second Nest Learning Thermostat (4th gen) in the next day or so, but in this situation, I'd like to know if you're having any issues, but only if you have already completed the installation.

Keep me posted.

Best regards,
Eduardo

[RobC18]

The installation of the second gen4 unit is complete.  It went quickly and without any issues.  My best guess is that the gen2 had an issue that is corrected on the gen4.

Thanks for your follow up and support.

Best,

Rob

[EduardoN]

Hi @RobC18, 

Thank you very much for confirming that you have already installed the second thermostat without any problems. If you have any more issues or need help with anything else, don't hesitate to reach out to this community.

Best regards,
Eduardo