Separate thermostat for heating and cooling

[Jabds]

Hello,

recently purchased a 3rd generation nest thermostat.  My heating is controlled by one of those old Honeywell 2 wire thermostats (red and white wire) and my cooling is controlled by the image shown below.  Currently I only have the nest hooked up to heat ( red in Rh and white in W1) with cooling dangling off to the side.  When the heat starts to kick on it sounds like the blower fan is cycling on and off and then after a few minutes the heat kicks on.  I have not heard this yet but my wife and father have both.  Is this a wiring issue? Do I need to connect the cooling side to this?  When I take a meter to the cooling wires I get 24vs, I have yet to try the heat but will when I get home.  I’m not sure if this a common wire issue that I’ve seen many posts about.  I also changed the air filter as well just in case.  Thank you for your help! 

[Jabds]

Also for extra reference, system is a forced hot air system.  If there are other details needed please let me know! 

[Jabds]

 

 

[Markjosephp]

Hello Jabds,

I'm sorry for the late reply, and thank you for taking the time to let us know about your inquiry. I'd love to help.

A power-related concern might be the reason why the fan short-cycles, as your thermostat isn't getting enough power from your heater. You might need to install a C-wire or the Nest Power Connector to help deliver consistent power to it.

Please take a look at this article to learn more about how the common wire works, and let me know if you have more questions.

Regards,

Mark

[Jabds]

Hi Mark,

Thanks for answering me back.  I hooked up the AC portion to the nest and I haven’t heard anything yet.  I just want to see what I’m thinking is correct.  I was able to measure a constant 24vs off my Rc line.  Because i now have my Rc connected and I think because it is internally jumped to the RH, it will now provide a more consistent voltage.  How does the power adaptor work?  Is it a 1 to 1 replacement for a C?  The only issue I’ve had so far now is if I pull the thermostat off the wall and it dies, once I put it back in it has the low battery warning and doesn’t connect to Internet.  I have to do a full restart for it to work again.  Battery voltage level is above 3.8

[Markjosephp]

Hi there,

Great troubleshooting so far! Thanks for the update on what you've done. The Nest Learning Thermostat doesn't require a C-wire to provide additional power. Your cooling wire helped to provide additional power to your thermostat, but there are some cases where you might still require one, as mentioned in the link above.

Removing the thermostat display from its base will drain its battery, but once it gets power, the Wi-Fi connection should reconnect once the battery level reaches 3.8V.

Thanks,

Mark

[Jabds]

Thanks again!  So is there a benefit to adding the power adaptor at this point? 

[Markjosephp]

Hello there,

Good question! As long as your thermostat is able to hold the power from your equipment, C-wire is an option. But in long-term use, installing C-wire or a Nest Power Connector would help to avoid power loss or any HVAC system issues mentioned in the article. At the moment, you can still use your Nest Thermostat with its current status and if anything comes up — you know where to find us.

Let me know if you have more questions in mind. 

Regards,

Mark

[Markjosephp]

Hey there,

I wanted to see if you still needed help. Please let us know if you have any other questions or concerns.

Thanks,

Mark

[Jabds]

Hi Mark,

I think it is working as it should for now.  I may add the power adaptor for peace of mind in case there is an extended power outage so I don’t have to reset my thermostat to factory settings or run the fan wire to the common instead.  Thank you for the help!

[Jenelyn_O]

Hi there,

Chiming in — it sounds like a plan! I'm glad that the issue seems now resolved. If anything comes up, please let me know as I'll be willing to help you further. 

Thanks @Markjosephp, for your assistance.

Best,

Jenelyn

[Jenelyn_O]

Hi Jabds,

I wanted to follow up and see if you still need help. Please let me know if you are still having any concerns or questions from here, as I would be happy to take a closer look and assist you further.

Best,

Jenelyn

[Jenelyn_O]

Hi Jabds,

I'm just checking in to make sure that you've seen our response. Please let us know if you have any other questions or concerns as I will be locking this thread in 24 hours.

Best,

Jenelyn

[Jabds]

[Filter: keyword] Jabds's post body matched "outage", board "Thermostats".

Post Subject: Re: Separate thermostat for heating and cooling

Post Body:

Hi Mark,

I think it is working as it should for now.  I may add the power adaptor for peace of mind in case there is an extended power outage so I don’t have to reset my thermostat to factory settings or run the fan wire to the common instead.  Thank you for the help!

Body text "outage" matched filter pattern "outage".

Post by User[id=297384,login=Jabds] has message uid 365347.

Link to post: Re: Separate thermostat for heating and cooling

[Jenelyn_O]

Hi Jabds,

Thanks for the follow up and for letting us know that the issue is now fixed. I duplicated this thread to the main one here. If you have any questions or concerns, I recommend updating and checking this thread when needed, as I'll be locking the main thread after 24 hours. 

Best,

Jenelyn