How to wire my nest thermastat without a common

[Mattssacre]

Hello. I have a older Nest thermostat. We had work done on are place and one of contractors removed the old thermostat. My friend tried to hook it up this new one using an online wiring schematic, but it's wrong. Only the AC works, but heater does not. Here are the pictures, I read it needs a common, but my wiring doesn't have the common colors. I have yellow, white, blue, red, brown. I can't check the units as they are on the roof of my condo and I don't have a ladder that can reach 2+ floors. Any help would be great! I've included pictures. Thanks

 

 

[Houptee]

Did you take pics of the old Tstat wires before they disconnected it?

Try disconnecting the wire to the G terminal.

So only use R Y W and see if the heat and ac work.

Possibly blue is your Common but without seeing the old T stat wiring you cannot be certain without going to the furnace on the roof.

Is this a Nat gas furnace for heat or a Heat pump ac system?

[Mattssacre]

No, I didn't even think about it. I thought they would be the ones to install the new one too, or at least label the wires. We've had issues with the contractors so they won't be coming back. It's a natural gas heater.

[Houptee]

I would take G blue wire off and then go thru Nest setup all over again.

W white is for the heat to kick on so it has to be configured in the Nest or heat will not work.

Did you tell Nest during setup a Gas Forced air heat system and AC?

[Mattssacre]

Ok. I'll try that when I get home. In the second picture, the "W" and "G" letters are yellow. That means there's a problem with them, right?

[EdwardT]

Hi folks,

@Houptee, thanks for the help!

@Mattssacre, how's it going with your Nest Thermostat? Still need our help?

Thanks,

Edward

[EdwardT]

Hey Mattssacre,

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]

Hi Mattssacre,

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

[Houptee]

Yes so you have to click learn more and try to force it to understand the W is connected. And check that your friend told it the correct type of system. Gas heat and ac with forced air ducts.

[Houptee]

This explains how to fix undetected wires during setup.

https://support.google.com/googlenest/answer/9244860?hl=en&ref_topic=9361783