Fan won't turn on

[SamDunham]

We just purchased our first house. I've had at least one 3rd generation Nest thermostat in my last two homes (one in my last one and two in the place before that). Never had any issues. Moved into the new house and the two thermostats are Honeywell Smart thermostats. I replaced the one upstairs with one of my Nest thermostats. Everything appears to work except for the fan. It refuses to turn on (cooling - can't test heating because it's entirely too hot outside). Here is the wiring for the Honeywell and the Nest:

Honeywell 

Nest 

I've checked the wiring, it all looks good. I've reset the Nest and didn't encounter an issue. Everything looks like it should be working. What am I missing?

[moralesvicente]

Hello SamDunham, 

Thank you so much for posting in this community. I’m sorry to hear that the fan of your Nest Learning Thermostat 3rd gen isn't working as you expected after installation. Don’t worry; it’s a pleasure to assist you. 

I appreciate the time and effort you took to complete the troubleshooting steps described in the post. To provide you with further information, please help me out by answering the following questions:

• Do you see an error code on your thermostat?

• Do you know when the last maintenance service and cleaning were performed on your HVAC system?

In the meantime, try to perform some troubleshooting steps:

Wire swap: For your safety and to protect your system, always turn off the power at the breaker or fuse box before you expose or adjust any wiring. Once the power is off, swap the Y1 cable with the G cable. Then restore power, turn on the fan, and call for cooling to verify that the fan runs.

If you feel uncomfortable performing this wire swap, we recommend reinstalling your previous thermostat and checking the fan functionality with that unit instead.

Let me know how it goes. 

Best regards, 

Daniel