Nest thermostat (Gen 1) blowing hot air when it is supposed to cool.

[Dandak]

I am trying to install a nest thermostat to an old system.  Here is a picture of the wiring in my old thermostat:

There is a bridge between Rc and R, and the red wire goes in Rc.  Y, W, and G.  All pretty standard from what I'm seeing online.  I do not have an O/B wire.  When I install the Nest (Gen 1), I put all the wires in their corresponding positions.  In the app I say that I have an Rc, Y, W and G wires.  Everything sets up, but it is blowing hot air when it should be cooling.  I did some checking and all the solutions say to mess with settings on the O/B wire, which I don't have.  I thought, maybe I should just say R instead of Rc.  I factory reset and re-did everything but said R instead of Rc.  Now I get an E294 error saying there is no power.  Below is a screenshot of my first configuration in the Google Home app:

I have a really old A/C system.  The unit is on the roof so I don't have a way of checking if it is a heat pump by seeing if it turns on.  I'm in an apartment complex.  Any assistance would be greatly appreciated.

[Ryan_G]

Hey Dandak,

Thanks for reaching out here in the Google Nest Community and for sharing these photos.

From the first photo, it seems that it is a conventional HVAC system and it should be wired the same way to the Nest Thermostat. I can also see a blue wire (unused) from the back. This could be a common wire that we can use and connect to the C terminal on the Nest Thermostat.

Let me know how it goes by replying to this thread.

Regards,

Ryan

[Dandak]

There is a blue wire back there, but when I connect it, the Nest says it isn't connected to anything.... I think.  It's been a while.  I'll have to see if I can get my landlord to set up the C wire.  It's been working great for the past couple weeks.

[MelbaDT]

Hey there, 

I understand. You might need to trace where the spare blue wire is connected on your HVAC's control board just to cover all the bases. Also, you could reach out to your landlord instead for the option of setting up a C wire. 

Best, 

Melba

[Ryan_G]

Hey everyone,

I'd like to jump in here and check if you've seen Melba's response. Let us know if you need more help by replying to this thread.

Thank you for your help, Melba.

Regards,

Ryan 

[Ryan_G]

Hey there,

Thanks for being here in the Google Nest Community. 

I'd like to bump in here and 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 thread in 24 hours.

Have a great day.

Best regards,

Ryan