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New thermostat. Thermo work fine but system won’t turn on.

Techman101101
Community Member

Hey all,

I just swapped out an old 3M thermostat that was working fine but the WiFi in it died.

We purchased a brand new Nest Learning thermostat. And I very carefully wired it according to the Nest instructions on my IPhone.

 

(Please see pics below of old wiring and the way I wired the new Nest thermostat)

The new Nest thermostat has power and appears to be working fine. I was able to hook it up to our WiFi just fine. Everything seemed OK until I ran the “Test” feature right at the thermostat.

Nothing happened at the system end. No A/C nothing.

I had to leave that house at that time but I am scheduled to go back there tomorrow morning and troubleshoot it.

This pic is the original old 3M thermostat that except for the WiFi was working fine.

8D388B95-B1C8-4DF2-AE49-53AF69037BAE.jpeg

 

This pic is EXACTLY how I wired the brand new Nest Learning thermostat.

  • DAD41750-0099-4573-94F7-40EFC3092D51.png

 

Just a guess here:

Notice the jumper wire between the RH and RC terminals on the old 3M thermostat. Could it be that I need the RED wire to go to RC terminal instead of the RH terminal on the new Nest thermostat?

I am posting this in the hopes one of you professionals out there might see something obvious.

Thanks in advance (smile)

3 Recommended AnswerS

Hello Cooling Wizard (smile),

Thank you VERY much for your reply.

I am getting ready to return to this job site at this very moment so your reply is perfectly timed. (Smile).

I will power off the system completely, move the red wire from RH to RC. Power back on and test again.

Hopefully this will solve the issue. I will let you know the results as soon as I have followed your suggestion.

View Recommended Answer in original post

Techman101101
Community Member

Hello Cooling Wizard,

That did it… simply moving the RED wire from RH to RC did the trick. The A/C and heater work perfectly now.

Thank you so very much (smile).

However, I would like to make a comment here:

Following the VERY nice Nest Wizard on my IPhone exactly TO THE LETTER was what caused this slight issue.

Because the old 3M thermostat had a JUMPER wire connecting RH to RC AND because in this systems case the RED wire went directly to RH AND because in the instructions it says (see pic below) “You won’t need them” (meaning any jumper wires). I followed the WIZARD instructions exactly and connected the RED lead directly to RH which (in retrospect) kept the system from getting power like it needed.

Anyway…. The new Nest thermostat AND the whole system is now working great again.

And I hope typing this issue out helps anyone else with the same problem (smile)

View Recommended Answer in original post

Most HVAC system thermostats use Rc as the primary connection.  Those whom understand the basic electrical characteristics will put the incoming voltage wire on Rh with a jumper to Rc.  When you are not familiar with how these systems work, you use the nest app and report the going to Rh. So, the app tries to not confuse you.  That is why it said Rh since you reported the red wire was connected to Rh. 

The logic should be, if you see a jumper wire between Rh and Rc and the thermostat cable wire is connected to Rh, the connection should be considered to be Rc and reported as so.

Ken, The AC Cooling Wizard  

NestPro and HVAC company owner

View Recommended Answer in original post

12 REPLIES 12

CoolingWizard
Silver Product Expert
Silver Product Expert

I am not sure why the installation suggested Rh.  Basically, Rc is used for a Cooling system, and Rh is used when there is a separate heating system. Old thermostats used a jumper from Rc to Rh to provide power to both sides of the thermostat. Try this, move the Red wire to Rc and then Retest. When you set up the system type, which did you choose? 

NestPro and HVAC company owner

Hello Cooling Wizard (smile),

Thank you VERY much for your reply.

I am getting ready to return to this job site at this very moment so your reply is perfectly timed. (Smile).

I will power off the system completely, move the red wire from RH to RC. Power back on and test again.

Hopefully this will solve the issue. I will let you know the results as soon as I have followed your suggestion.

Techman101101
Community Member

Hello Cooling Wizard,

That did it… simply moving the RED wire from RH to RC did the trick. The A/C and heater work perfectly now.

Thank you so very much (smile).

However, I would like to make a comment here:

Following the VERY nice Nest Wizard on my IPhone exactly TO THE LETTER was what caused this slight issue.

Because the old 3M thermostat had a JUMPER wire connecting RH to RC AND because in this systems case the RED wire went directly to RH AND because in the instructions it says (see pic below) “You won’t need them” (meaning any jumper wires). I followed the WIZARD instructions exactly and connected the RED lead directly to RH which (in retrospect) kept the system from getting power like it needed.

Anyway…. The new Nest thermostat AND the whole system is now working great again.

And I hope typing this issue out helps anyone else with the same problem (smile)

Most HVAC system thermostats use Rc as the primary connection.  Those whom understand the basic electrical characteristics will put the incoming voltage wire on Rh with a jumper to Rc.  When you are not familiar with how these systems work, you use the nest app and report the going to Rh. So, the app tries to not confuse you.  That is why it said Rh since you reported the red wire was connected to Rh. 

The logic should be, if you see a jumper wire between Rh and Rc and the thermostat cable wire is connected to Rh, the connection should be considered to be Rc and reported as so.

Ken, The AC Cooling Wizard  

NestPro and HVAC company owner

Ryan_G
Community Specialist
Community Specialist

Hey everyone,

 

Thanks for being here in the Google Nest Community.

 

It's nice to see that we are sharing thoughts and ideas here and everyone can learn from one another. Sending our huge thanks to Techman101101 and CoolingWizard for a great discussion. 

 

If you have any other questions, feel free to post it here. 

 

Also, about mistakenly pressing the solution button, we'll take this as feedback and check what we can do more to create a better product and services.

 

Regards,

Ryan

MelbaDT
Community Specialist
Community Specialist

Hi, 

 

We haven't heard from you in a while so we'll be locking this thread if there is no update within the day. If you have any new issues, updates or just a discussion topic, feel free to start a new thread in the Community.

 

Best, 

Melba

Techman101101
Community Member

First, I want to apologize… it was actually Ken the Cooling Wizard that corrected this issue and NOT myself. I accidentally hit the wrong box and I don’t see anyway to reverse that.

Sorry Ken… (maybe you can change it on your end?)

Techman101101
Community Member

(Now about the initial issue)

Hello Ken The Cooling Wizard,

Thank you very much for explaining that. (Smile)

But since the WIZARD and this kit is set up so that the average home owner can swap out their own thermostat and they are not professional HVAC professionals like yourself, how are they supposed to know what you stated unless the WIZARD tells them? (Smile)

I do I.T. for a living and I know just how expensive it is to alter or correct a detailed Wizard like the one Nest had written for them.

So I understand that that is probably NOT going to happen until they do a complete rewrite.

Anyway, thank you VERY much Ken for correcting the slight error in the Nest Wizard. Human input is still important until true AI exists. (Smile)

Techman,

You raise a pretty good point.  However, think about this please.  Many people become DIY people for many reasons. Some to save money, others to advance their personal skills and knowledge, and the best reason, they simply love to do themselves. 

Manufacturers do the best they can. And, when creating a product for DIY, they try their best to cover most situations. What is not easy, is to explain the ins and outs of HVAC control systems. The manufacturer cannot assume you know all about your system. For example, they ask you if your heating system a separate system or do you have a heat pump.  This is about all that can be done.  To cover the other areas, you have Google Nest Customer Service and this public forum where all of us try to help the others.  

Having said this, I know, and I have seen HVAC techs mix the wire colors and in some cases use manufacturer custom programmable thermostats to create confusion and require a call for service.  Thermostats are typical technology and smart thermostats fail; some sooner than others. 

I wish you the best, and thank you for reaching out.

 

Ken, The AC Cooling Wizard

 

NestPro and HVAC company owner

Jeran
Community Specialist
Community Specialist

Hey there Techman101101,

I'm glad to hear that CoolingWizard was able to help you out! In that case, did you have any other questions or concerns that we can address?

Thank you for helping out on this thread, CoolingWizard!

Best regards,
Jeran
 

Ryan_G
Community Specialist
Community Specialist

Hey everyone,

I'd like to jump in here and check if you've seen CoolingWizard's response. Let us know if you need more help by replying to this thread.

Thank you for your help too, Jeran.

Regards,
Ryan 
 

Yes thank you (smile).

Ken, The AC Cooling Wizard WAS able to compensate for the slight FLAW in the NEST setup Wizard.

If you carefully read my above posts and carefully look at the wiring pictures that I posted and if you are VERY familiar with the NEST setup Wizard you will see the slight flaw.

Anyway, thanks to Ken for pointing out the correct wiring setup.

(PS. As I stated above…. Ken, The Cooling Wizard is the HVAC professional that was nice enough to point me in the right direction. I mistakenly hit myself as the solution. Some times my IPhone touch screen is over sensitive. Perhaps the forum moderators can correct this as there is no option to change it as a simple user.)