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Please help me. Where I have to connect W2 wire?

kyounghwan
Community Member

My 0ld thermostat has wires connected to R G Y W W2.

I am trying to replace my old one with Nest Thermostat. My Nest has 6 sockets R, G, Y, W, C, OB. It does not have W2. Should I connect W2 into Nest OB? Or my nest is not compatible with my old thermostat.

Thank you a lot for your help.

18 REPLIES 18

CoolingWizard
Platinum Product Expert
Platinum Product Expert

Kyounghwan,

it looks like you must have a nest thermostat and sadly those do not support multiple heating types and multiple cooling types. In order to get support for two different types of heating sometimes called two stages. You would need a nest learning thermostat. The nice thing is that Google provides a Nest compatibility checker that if you had use that before you purchased your nest, you would’ve learned that you would need a nest learning thermostat..

https://store.google.com/us/widget/compatibility/thermostat

Ken, The AC Cooling Wizard

Ken, The AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner. If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

kyounghwan
Community Member

Hi Ken,

Thank you a lot for your quick reply and help. I did the check and the checker says working with three types including nest thermostat. And it was cheapest and that is why I went for it.😀 But looks like I need to upgrade it to nest learning thermostat.

Thanks again!

Best Regards,

Kyounghwan

CoolingWizard
Platinum Product Expert
Platinum Product Expert

Admittedly, I don’t recall the original nest thermostat, but does it have a connector for a star *. if it does, then it can be used to connect a two stage heating on it but if you will simply use the Nest app and follow the step-by-step installation instructions that are provided when you provide all the information to the configurator it will let you know where to put the wires

Ken

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner. If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

Yes it has * star, OB*! That is great. I should try nest app to make sure.

Ken! Thank you for your expert help!

Hmm I have an orange wire going to O/B * already. The white wire has no home.  In the app it asks for which spots were connected to the old thermostat and the white wire was connected to W2.  Any help would be great!

EdwardT
Community Specialist
Community Specialist

Hi folks,

 

@CoolingWizard, thanks for the help!

 

@clarkbecker, thanks for letting us know. Could you share a photo of how your previous thermostat and your Nest Thermostat is wired?

 

Thanks,

Edward

EdwardT
Community Specialist
Community Specialist

Hi clarkbecker, 

 

It's me again. I wanted to check back in to see if you have other questions and concerns. Feel free to let me know if you do. 

 

Thanks,

Edward

EdwardT
Community Specialist
Community Specialist

Hi clarkbecker, 

 

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 in 24 hours.

 

Thanks,

Edward

CoolingWizard
Platinum Product Expert
Platinum Product Expert

The “*” is a programmable connection Point. When you use the Nest Installation configuration tool, it will direct your to put the W2 wire on the * connector.

The AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner. If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

Hey folks,

We appreciate your help here, @CoolingWizard.
@kyounghwan, I wanted to follow up and see if you are still in need of any 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.

Thanks,
Mel

EmersonB
Community Specialist
Community Specialist

Hi everyone,

 

@kyounghwan how's it going with your Nest Thermostat?  I'm dropping by to ensure that everything is covered here and wanted to follow up to see If you have other questions and concerns.

 

Thanks for lending a hand, Mel and Ken.

 

Best,
Emerson

Hi Ken, 

I just installed Nest Thermastat, I connected W2 into OB*. Looks all good but when I turn on the heat, I can hear that my furnace runs, which is good. However, the room temp never reaches to the point I set. I actually don't get heat air. It just air. Nest says  NO power with M20 error code. I checked wire in setting. All wires are blue color and no grey, which means connections are all good. Do you happen to know why I am getting this No power M 20 error? is that why I am not getting heat air even though my furnace runs 

CoolingWizard
Platinum Product Expert
Platinum Product Expert

Hello, the M20 specific error is related to the missing primary power in. This is confusing because the system is running and operating and therefore there should be power input present. As for your heat not working, this is puzzling as well. You may have one of your heat strips burnt out and not actually working anymore so you’re not getting enough heating BTUs. When there are multiple heat strips set inside the furnace, they cannot all start at one time. So there is a device called a sequencer that starts with one then it wait a moment and then starts the second egg starts the third after that, etc. it’s either a bad sequencer or you have a heat stripped it’s not heating properly. The only thing the nest could be causing is an incorrect application of the G wire. The nurse should not be turning on the blower when it calls for heat or air conditioning. The air handler will handle that by itself. When blowers are turned on, they’re turned on at the higher speed when you do energize the G wire. And the furnace operator blower at a lower speed typically medium speed. If you have a if you have a clamp meter, you can measure the input current going into the system, and see if you can detect the increase in amp draw, as each of the heating elements is turned on by the sequencer.

Ken, The AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner. If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

Hi Ken, 

Thank you always for your reply. I am sorry that I confused you. In fact, heating works fine. As I just replied to Ebedia comment, I get No power and M20 code. My question to her was what is the significance of C-wire. What if I just go without C-wire connected? Does it impact the performance of my heating/cooling system? As long as that does not impact the performance and does not damage my heating/cooling system, I think I will just stay with what I have, which without C-wire connected...

Thank you.

EmersonB
Community Specialist
Community Specialist

Hello kyounghwan,
 

The C wire provides constant power to the Nest Thermostat. Like what I've mentioned in my previous reply, that type of Nest Thermostat requires a C wire connected. If there's no C wire it might work but it won't last long and you'll get an error code or message. Hit this link to know more about C or common wire. Your other option is to get a Nest power connector. This will serve as C wire for that type of Nest Thermostat. Let us know if you have more questions in mind.

 

Best,

Emerson

EmersonB
Community Specialist
Community Specialist

Hello kyounghwan,

 

Thanks for getting back to us. To confirm, what type of Nest Thermostat do you have? In case you have the Nest Thermostat with a mirror screen and a touch panel on the side, that one requires you to have a C wire connected or else you'll have an error message sooner or later. One of them is the M20.

 

Regards,
Emerson

Hi Ebedia,

Yes that is what I have. And I already have No Power and M20 code. My question is what if I don't want to have C wire connected. Not having C-wire connected affect wi-fi connection? because my nest thermostat does not connect to Wi-Fi. Also more important question is whether No C-wire connected affect performance of my heating/cooling system? As long as it does not affect performance of my heating/cooling system, I think I will stick with it. So far heating system works fine. Just the annoying No power and M20 error. But I would like to understand the importance of C-Wire....

Thank you a lot. 

Thank you so much. 

CoolingWizard
Platinum Product Expert
Platinum Product Expert

kyounghwan,

alternating current(AC) electricity works with two wires, one is LINE and the other is NEUTRAL wire.  In the past all the thermostat would do is take that incoming line voltage on the R wire and switch it to one of the other wires to go back to unit activating a function. For example, if R connected to the Y terminal, it will turn on the air conditioning system . If the R is connected to the W terminal, it will turn on the heating system

Now, when it comes to smart thermostats they are computer controlled thermostats. The smart thermostats needed power for the microprocessor; to achieve this they used AA or 9V batteries. As more functions and capabilities were introduced the battery capacity could not keep up. Consumers would not want to change the batteries every week. Basically a power source was needed to keep an internal battery charged. Luckily, 24 V of AC power were available on the R wire. All we would need is the Neutral side too; this is the Power Common.

The HVAC equipment has the step-down transformer that changes 120V AC or 240V AC down to 24V AC. All we need to do then is get the Neutral side on a wire to the thermostat. Sometimes there’s a spare wire behind the thermostat that can be used. Sometimes we would have to put a whole new cable in with more conductor wires, or you can use a Nest power connector. The goal is the same, get the Power Common to the thermostat. Without the Common, the lithium battery will discharge. As it does discharge, in an effort keep doing the basic functions, the Nest Learning Thermostat starts turning off functions to keep the basic functions working; controlling the HVAC equipment. 
I hope helps you to understand. 

Ken, The AC Cooling Wizard

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner. If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.