Nest Thermostat 2020 showing wrong temperature.

[Aegius]

So I recently purchased three nest thermostats to install in the house. I also purchased an adapter to provide c wire voltage. My first two installs went perfect and operate flawlessly the third one has an extremely strange problem that Google senior support staff couldn't figure out.

After installing it shows the current temperature in the house at 82°, even though multiple thermometers are showing 70°. I tried attaching one of the other nest thermostats and it immediately went up in temperature to 82°.

I managed to figure out through trial and error that when I shut off the HVAC system the temperature drops on the nest thermostat to the correct temperature.  the wiring is correct the same as all the other devices I installed in Google senior support agreed the wiring is correct. They suggested I reach out to an HVAC technician.

Any ideas from the community would be well appreciated.....

 

 

[CoolingWizard]

It may just be the angle of the picture, but it looks like you have two wires going into our and the way those are designed only a single wire should be in each connector and that R is therefore connected to C. This would be bad and can damage the logic board of the thermostat.

Ken, The AC Cooling Wizard

[Aegius]

Yes the R has 2 wires going in. The c wire has 2 leads the white lead goes into the c slot and the striped wire goes together with the red wire into the R slot. All the other thermostats are set up like this and work fine. If i don't do this the device wouldn't power on.

[CoolingWizard]

I am afraid that wiring scenario does not make any sense. You have to understand that if R is directly wired to C, you will cause a direct short between the two leads of secondary sides of the transformer. In a thermostat you typically do not have more than one wire connected to a single terminal with the only exception being a jumper between RC and RH when they are separate systems. If you short the R and the C together will probably blow the fuse on the step down transformer, or you will burn out the step down transformer in the air handler

Ken, The AC Cooling Wizard

[Aegius]

I believe I figured this one out. The manufacturer of the power adapter I was using switched the wires somehow when being manufactured. Switching the wires at the thermostat seems to have resolved the issue. Now that Google makes a C wire adapter I'll probably just replace these adapters with those instead.

[CoolingWizard]

What is the brand and model number of the power adapters that you were using? I’d like to look them up in my manufacturer cable manuals that I have and I want to verify the wiring of that so I can make sure nothing is going on that’s gonna damage your system or your thermostat.

The Cooling Wizard

[Aegius]

 

 

[Aegius]

24 Volt Transformer, C Wire... https://www.amazon.com/dp/B07DJ7RHS5?ref=ppx_pop_mob_ap_share

[EmersonB]

Hi folks,

@Aegius we're glad to hear that you're able to resolve it and sorry for the delay. I'm dropping by to ensure that everything is covered here. Let us know if you have more questions in mind.

I appreciate the help, Ken.

Regards,
Emerson

[Jhonleanmel]

Hi there,

Chiming in to see if you still need assistance with this. Let us know if you have additional questions ― we'd love to help.

Best,
Mel

[Jhonleanmel]

Hi everyone,

Just one quick final check in here since activity has slowed down. We'll be locking the thread in the next 24 hours, but if you still need help, I would be happy to keep it open. If there's more we can do, just let me know.

Thanks,
Mel