Replacing Honeywell with Nest

[Jlcorralm]

The Honeywell Thermostat works fine with only 4 wires, current settings on heat and it waits probably a minute to start and then everything is fine.

With the nest thermostat it starts immediately and doesn't wait but the air is cold, I tried to swap the O/B settings during the setup and it is the same, what I'm doing wrong?

Current Honeywell Configuration, it works fine with only 4 wires

Tried using the O/B wire and even C wire

[sporfrog]

It looks like in the original picture (Honeywell) the orange wire is not connected. Yet with the Nest it is.  Was that orange wire used before?  If not it should not be used with the Nest either.

I know this seems contrary to above, but it is different...

Is there any chance that blue wire is connected to C (common) at the HVAC system? Nest thermostats often work better if a common wire is used. If it is connected at the HVAC system to a C (common) terminal, and you are sure, it can be connected to C at the thermostat.

[Jlcorralm]

Thanks for your reply, I just checked the wires on the Trane air handler where the wires connect to the thermostat without using the Orange and Blue wires, looks like my system doesn't have a C wire, I just ordered a C wire adapter from Amazon, that will arrive tomorrow and I will try that.

I don't know why the current Blue and Orange wires are not connected to the unit but looks like are not needed because everyhting works perfect with the Honeywell Thermostat

[sporfrog]

Regarding the Orange wire....

In the picture of the Honeywell thermostat connections, it appears that the orange wire is not connected. However in the picture of the Nest thermostat it is connected.  If the Nest thermostat thinks the orange wire is functional on the O/B terminal it will use it,  possibly causing unexpected behavior. My point on the orange wire is that IF it was not used with your old thermostat it almost certainly should not be used with the new one. Maybe I am missing something?

[mkormendy]

Did the C wire adapter fix your problem?

[Tim1245]

Hi,

I have the following Honeywell Pro Thermostat And what to know if the nest thermostat will work and the correct wiring...