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Did my Nest base fail?

JD83
Community Member

I have a Nest 2 that has served me well for years. (I have a 3rd gen on the way). I moved to a new place and brought my Nest with me. I have a single stage Trane heat pump with single stage electric aux/emergency heat.

My existing thermostat that works is an Emerson 1F79-111.

I connected the Nest per the instructions and based on where the existing wires were on the Emerson.

[G to G]  [Y to Y]  [R to RH]  [C to C]  [O to O/B]  [W2 to W2/AUX] 

The Heat and Aux Heat work and engage when needed. However when switching to Cool mode the system comes on but it's still heating. I verified on the old thermostat it is an O wire for the reversing valve. I also traced the wires to the air handler to make sure I had them matched up correctly. Verified on air handler that it is connected to the O terminal as well.

I contacted Nest support and they had me change the O/B setting to B but that made no difference so we changed it back. They recommended I buy a new thermostat.

I reconnected the old thermostat and I'm able to switch to cooling mode.

Did my Nest bite the dust? Should I try with the 3rd gen when it gets here or am I missing something?

 

1 Recommended Answer

CoolingWizard
Platinum Product Expert
Platinum Product Expert

When I Install Nest Learning Thermostats on Heat Pump, I put the Power IN Conductor on the RC terminal. You might want to try that. As for your O wire, some systems are B models. Your system might need the reversing valve activated for cooling and not for heating or vice versa.  Go into setup and change the orientation of the O terminal.  
Keep in mind that switching from heating to cooling causes a delay for the Mode switch to be initiated by the control board in the air handler. 
it sounds like the settings are still not correct.  I can give you a test that might not go over well with others.  

turn power off to the indoor air handler.   Using the wires, connect the R wire to the Y wire.   Turn the power back on, Do you get heat or cooling? ,  If so, turn power off again, add the O/B wire to the R and Y.  Turn power on and see if it switches to opposite mode.  Keep in mind when the power is turned off on a running outdoor unit, there is a time delay before the system comes back on, so be patient. 

If the system is in AC cooling mode with just the R and Y, you need to energize the O wire for heating. On heat pumps I put the R wire on Rc, not Rh.  

Ken, The AC Cooling Wizard, 

 

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

View Recommended Answer in original post

4 REPLIES 4

CoolingWizard
Platinum Product Expert
Platinum Product Expert

When I Install Nest Learning Thermostats on Heat Pump, I put the Power IN Conductor on the RC terminal. You might want to try that. As for your O wire, some systems are B models. Your system might need the reversing valve activated for cooling and not for heating or vice versa.  Go into setup and change the orientation of the O terminal.  
Keep in mind that switching from heating to cooling causes a delay for the Mode switch to be initiated by the control board in the air handler. 
it sounds like the settings are still not correct.  I can give you a test that might not go over well with others.  

turn power off to the indoor air handler.   Using the wires, connect the R wire to the Y wire.   Turn the power back on, Do you get heat or cooling? ,  If so, turn power off again, add the O/B wire to the R and Y.  Turn power on and see if it switches to opposite mode.  Keep in mind when the power is turned off on a running outdoor unit, there is a time delay before the system comes back on, so be patient. 

If the system is in AC cooling mode with just the R and Y, you need to energize the O wire for heating. On heat pumps I put the R wire on Rc, not Rh.  

Ken, The AC Cooling Wizard, 

 

NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
If my answer solved your problem, click Recommend this Answer below, and If it helped you, please give a Kudo.

Thanks! I confirmed with the wire tests that O needs to be energized for cool.

My new 3rd gen learning thermostat came in today and I connected it the same way and it works correctly with heat, cool and aux. I guess the old one finally failed. 

5E340AF8-220D-42BD-B16D-BD33D1F882D9.png

Jhonleanmel
Community Specialist
Community Specialist

Hey folks, 
 

@CoolingWizard, thanks for the help.
@JD83, awesome — glad to hear that your issue is fixed. It looks like we can consider this one complete, so I will lock the thread shortly unless I can help out with anything else. 

Best, 
Mel

Hi everyone,

As we got our resolution here, I'm going to mark this thread as resolved. I'll be locking this thread if we won't hear back from you in 24 hrs. Should that happen, feel free to create a new one if you have more questions or have other concerns in the future.

Cheers,
Mel