Nest Thermostat offline and low battery message

[KMclean19]

We have had our nest thermostat for several years and have had no issues up until yesterday.  It started with the downstairs and now the upstairs unit is having the same issue.  Both units are going offline and shows a low battery message.

I removed the units and charged via a USB but this seems to only be a temporary fix as the batteries continue to drain.

Currently our wire connections are the following:

Y1 - Cool (yellow)

G - Fan (green)

Rc - Power (red)

W1 - heat (white)

A few troubleshooting tips I have read is to connect a C wire.  We do not have any extra wires, but was wondering if we could remove the Rc wire and plug it into the C wire slot? I was concerned because this is a red wire and most articles mention a white wire. 

Any advice is greatly appreciated.  Hoping I can figure this out without calling an Electrician or HVAC tech.

Thanks!

[HVAC]

You can not use the red wire for C thats meant to be connected on nest R or Rc or Rh. that’s the power side of your 24 volts & need Common/C to complete the circuit so nest has 24v. All the time So you’re missing a C wire that powers up the nest & crucial for WiFi & other function to keep working without acting up & stopping because of internal battery running low. At times you might have an extra wire in that bundle of wires either wrapped up on outside or inside with the rest of the wires. If you only have 4 wires you can power up the nest with the existing 4 wires but needs to be required at you furnace control board & you’d lose function of running the fan by itself. Pics of whats connected on nest sub base mounting plate & at furnace control board would help to wire it up correct. Good luck 

[Jenelyn_O]

Hi there,

Thanks for reaching out. I'm sorry for the delay. In most cases, Google Nest thermostats can charge their built-in battery using your heating and cooling wires. But, there are situations where you may need to connect the Nest Power Connector or a common or C wire to consistently deliver power to your thermostat.

A common wire is a wire that's dedicated to delivering constant power and stabilizing the flow of current into the thermostat. Unlike the other wires connected to it, a common wire doesn't control any heating or cooling functions.

Instead of C wire, you may use the Nest Power Connector, as its substitute. 

I appreciate the help, @HVAC.

Best,

Jenelyn

[jbagri88]

I also have the same issue. I only have 4 wires. Can you send us a diagram of how it should be connected so the nest gets power and the system works properly too?

[Jenelyn_O]

Hi jbagri88,

I'd like to help. Could you please take a photo of the wires you have on your thermostat, and share it with us? Ensure that the labels are visible. It will help us to check your system's wiring configuration. 

Thanks,

Jenelyn

[jbagri88]

How do I share it because it says I don’t have permission to attach a photo. 

[jbagri88]

Never mind. Figured it out. It is below:

[Jenelyn_O]

Hey jbagri88,

Thanks for sharing the photo above. You have a conventional system and it looks wired properly. What messages or codes do you receive? If you're encountering power issues, try to move the red wire from Rh to Rc terminal, but make sure to turn the power breaker off before touching the wires. Also, provide your thermostat's power readings. 

You can follow this guide:

1. Go to your thermostat Quick View menu.
2. Go to Settings.
3. Look for Technical Info.
4. Select Power.

Best,

Jenelyn

[jbagri88]