Nest running heat pump - cooling but not heating

[jlehm]

Nest Gen 1 running a heat pump.

System works properly with old thermostat.

Wiring transferred from old thermostat in same wire positions.

Cooling turns on air handler and compressor and cools the home.

Heating turn on the air handler but NOT the compressor. Air is room temperature.

No wiring error codes.

Settings-Thermostat-Wiring: Y = Heat/Cool, G = Fan, C = 24V Common, R = Power, W = Empty, O/B = Heat Pump

[jlehm]

Standard Nest, not Gen 1 learning.

[AxelD]

Hi jlehm,

Sorry to hear about this situation with your Heating, No worries, help is here! Based on the wiring information you provided, it seems you don't have a W-WIRE which controls heating. Let's try changing the O/B WIRE settings:

1. Open the Home app Google Home app.
2. Tap your thermostat.
3. At the top right, tap Settings .
4. Select Thermostat.
5. Scroll until you find Heat pump. It should show which wire configuration is currently selected.
   If the O option is highlighted, select B.
   If the B option is highlighted, select O.
6. To make sure the issue is resolved, test your heating and cooling again.

If the troubleshooting steps above don't solve your issue, please get a local professional to install a W-Wire because that might be the reason why is not blowing hot air.

Regards,

Axel.

[jlehm]

I now have additional information.

If fan is selected from the thermostat to only circulate air in the home - no heat or cooling - heating is activated.

If cooling is selected, the compressor will come on and cool the home. Once the target temperature is reached, heat turns on.

[AxelD]

Hi jlehm,

Sorry to hear about your cooling still not working. No worries! Here are some additional troubleshooting steps you can try in this article: Troubleshoot strange heating or cooling behavior.

Please take a look and let me know how that works.

Regards,

Axel. 

[jlehm]

Thanks Axel.

Because the thermostat identifies the connected wires in this way

Settings-Thermostat-Wiring: Y = Heat/Cool, G = Fan, C = 24V Common

Can I switch the wires in G and C and test again without causing damage?

On the old thermostat, G is a green wire which should be 24V Common and C is not connected.

I'm not sure why Nest identifies G as fan and C as 24V Common.

[AxelD]

Hi jlehm,

Thanks for your reply! To help me get a better picture of what's happening, do you mind sharing a photo of your wiring? Also, I have a few questions:

• What kind of systems do you have?
• Can I get the Heat Pump information? E.g. Make and model.

Additionally, please don't swap those wires, that might cause damage to your system. C-WIRE only should be connected in the C-PORT in the Nest Thermostat. 

Regards,

Axel.   

[jlehm]

Single heat pump. Heat exchanger outside, air handler in attic.

Existing thermostat with wiring that operates the heating and cooling correctly.

Nest thermostat we are trying to install.

Wiring that gives the behavior documented above in the thread.

Wiring in the attic by the air handler where dissimilar colors are connected.

Because the C wire was not connected in the existing thermostat, I don't have confirmation how it connects to the unit. The attic wiring shows dark blue C wire connected to black. Nest identifies this connected wire as 24V common and green as Fan. I would expect green to be 24V common as it is on the existing thermostat.

[AxelD]

Hi jlehm,

Thanks for the reply! Checking the photo of your previous and current wiring. It seems you have the next wires: R, W, Y, and G. I'm using the letter tags for the Conventional system (in your old thermostat).  Please try the next troubleshooting steps:
 

• Disconnect the C-WIRE and not re-connect it. 
• Swap the Y Wire with the W Wire and run the cooling. 
• If it doesn't work, move the W wire to the O/B port and try running it that way.
   

Keep me posted.

Regards,
Axel.