Google Nest Wiring - No Yellow (Cooling) Wire

[LC4]

Hello-  Replaced a 2004 thermostat with the Nest.  Electric Ducane  with AC and heat with 4 wires at thermostat.

Red (Power)

Blue (Common)

White (Heat)

Green (Fan)

I have an outside AC unit compressor that worked prior to the change to the Nest.  The Nest thermostat does not recognize cooling, only heat and only the heat works now.   I checked the wiring at the furnace and the Blue (Common) is wired to the Yellow and White (2) wires going outside to the AC unit compressor.  Any thoughts or help appreciated. Thanks.

[Patrick_Caezza]

Can you post a picture of the original thermostat's wiring?

[LC4]

Unfortunately I can’t find the photo.  I do remember however that there was a red jumper wire on the old thermostat. 

[Patrick_Caezza]

No worries.

Can you instead post a picture of the wiring on the terminal block on the control board in the furnace/air handler?

[LC4]

It’s in the attic and very difficult to get to and the control board is facing inward, so I could not take a photo.  I was able to trace wires and all colors were connected/wire nut at furnace to corresponding color except blue common which was wire nutted to the yellow and white going out to the compressor.  

[LC4]

I fixed the issue.  The HVAC installer used blue wire for the yellow that typically goes out to the AC compressor. I placed the blue wire in the Y slot on the Nest. Most important step is to “Add/Remove wire” in the Nest App settings to let the Nest know that I was adding the blue wire into the Y slot for cooling and removing the blue wire from the C slot. 

[Markjosephp]

Hello folks,

I wanted to ensure that everything was covered here.

Thanks for the help, @Patrick_Caezza.

@LC4, I appreciate you posting and updating us on your efforts to address your concern and find a fix. If there’s anything else I can help you with, please let me know. Otherwise, this thread will be locked within 24 hours.

Regards,

Mark