Can anyone help with my c wire blues with my Google Nest? I have two ACs, one for downstairs and another one for upstairs. I recently upgraded my battery operated t-stats with Nest. My old ones used only 4 wires, the blue wires were tucked away. On the first one, after connecting all 5 wires, to include the blue unused wire at the furnace and the tstat, Nest recognized all wires and is working fine. The second one, not so. It shows no power detected at C terminal. I did all the troubleshooting that I found all over the internet to no avail. I swapped the green and blue wires at both the furnace and the tstat to see if the blue wire is damaged, it works. I swapped the tstats same issue. I returned both tstats and got new ones, same problem. Update: I will upload the right images when I get back home. But to answer your question, with the multimeter at the furnace from R to all individual connections (Y W G AND C) it reads 28v. At the tstat level, all read the same with the exception of C that reads very low voltage, like 1v or some other low number. The culprit model is a Goodman that was installed in 2017. The furnace model is GMS80804BNBE. Coil and compressor is a 16 seer 4 ton.
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I went and bought a new 18-5 wire and connected it to the furnace and tstat. It worked!! Now when I was in the process of removing the old wire to replace it with the new one, I discovered that the old wire was not one continuous wire, it was two wires joined with wire nuts... And, you probably guessed it, there were only 4 wire nuts. The blue wires were not joined!! I don't know why someone would do that, but hey, it all ended well for me. Thanks all for your suggestions and contributions.
