thermostat wiring

[notbobg]

I bought a Nest learning thermostat and when I took the cover off of my old thermostat (Carrier Zonecc0usi01b) the wiring was not what I expected. Only a red and white wire is hooked up.  Yes my A/C and Heater work. The other wires were tucked away in the wall. Do I hook the Nest by following the colors anyways? Any help would be appreciated. 

[CoolingWizard]

@notbobg ,

One of the things that manufacturers of HVAC equipment started doing was trying to compete against smart thermostats by creating a proprietary interface. Your system was converted to use one of these proprietary, digital, communicating interfaces that only requires two wires. However, those same systems often have the conventional 24 V AC control systems also on the control boards. What you will have to do is go to the air handler and to the outdoor unit and verify that it has the typical interface that is uses. R, Y, W, C, G.  If it does, you can convert back to using a conventional interface and thus switch over to a nest thermostat. If you can go to your outdoor unit and get me the model number, and give me the model number of your indoor unit, I can look it up and see if the control board has the ability to be switched back.

AC Cooling Wizard 

[notbobg]

The outdoor AC is a Trane Model 4TTB3060D1000BA..i will go up into the attic to check the air handler.

[CoolingWizard · Accepted solution]

Your outdoor condensing unit has a standard and conventional control system. So unless they’ve added additional Sentri module it’ll be able to be converted

AC Cooling Wizard.

[notbobg]

So I bypassed the EIM board in the attic and wired correctly to proper terminal. Do I need to do anything to ac outside? 

[Jake]

Hey notbobg,

Thanks for the help CoolingWizard.

I wanted to check in and see if you managed to see CoolingWizard's post. Please let me know if you have any questions from here. I would be happy to assist, and make sure you are good to go.

Best regards,
Jake

[Markjosephp]

Hi notbobg,

I'm checking back in — how's it going? Still need our help?

Thanks,

Mark

[Dan_A]

Hello again,

We haven't heard from you in a while so we'll be locking this thread if there is no update within 24 hours. If you need assistance or want to discuss topics, feel free to start a new thread.
 

Cheers,

Dan

[CoolingWizard]

Ok, the Y wire and the C wire is what is connected to the outdoor unit.  You should have seen a cable at the attic unit and going outside.  Here is a picture of the typical connections. If the wire going outside was connected to the EIM we need to make sure what is outside.  

The B wire is the COMMON. 

AC Cooling Wizard