Nest Learning 3rd Gen Fan Coil Compatibility

[MattLomb]

Hi,

I am trying to install a Nest Learning Thermostat 3rd Gen in my condo. I wired it as per instructions but can't seem to get cooling to work.

I am not expert, but I know that my heating/cooling system is a Climetec TD-DFA-4 controlled by Honeywell TB7-100A-1000 previously. It had C, G, Y, RC, W1, G2, G3 wires.

I would really appreciate any help in getting this work - or is my system just not compatible with Nest?

Thank you,

Matt

[chaconmorales]

Hi @MattLomb,

Thanks for reaching out to the Community. I am sorry that you are having issues with your Thermostat cooling feature. But no need to worry. Let’s check it out.

Before we get started with further troubleshooting, let me ask you some questions

• Does the thermostat display show any error codes or messages?
• Are you able to share a picture of your wiring?

Here are some steps you can try to troubleshoot the issue:

Basic Checks:

• Power: Ensure your AC unit is turned on and receiving power. Check the circuit breaker or fuse box to see if a tripped breaker or blown fuse is interrupting power supply.
• Thermostat: Verify that your thermostat is set to "cool" mode and the desired cooling temperature is lower than the current room temperature.
• Check Wiring:
  • Turn off the power to your HVAC system at the breaker box for safety.
  • Based on the information provided, your Nest Learning Thermostat might be compatible with your system, however you may need to contact a Nest pro and have them check your system to confirm if it is compatible.

However you can check the following article to verify your Nest thermostat compatibility.

Please keep me posted. 

Best regards,

Mario

[MattLomb]

Hi Mario,

I have attached the before and after wiring photos below. I do not get an error message whatsoever on my Nest. However, I had an HVAC technician come in and they confirmed that Nest is not turning on the cooling actuator even though Nest thinks it is on.

I have followed the Nest compatibility checker and it said that Nest is compatible based on the wiring. Considering that the setup was successful, I am not sure why Nest is not working with the actuator.

[chaconmorales]

Hi MattLomb,

Thank you for following up and sharing pictures of your system. I understand your frustration with the device that does not work. I apologize for the inconvenience you're experiencing.

Based on the pictures and information provided, your system has more than one fan wire, you should contact a Nest Pro to have your Nest Learning Thermostat installed. Incorrect installation settings can damage your system, your thermostat or both. Some systems that need to be installed by a Nest Pro include systems with G2, G3, GM, or GH wires.

However you can check the following article to verify the Fan compatibility with Nest thermostats.

Let me know if you need further assistance.

Best regards,

Mario

[MattLomb]

Hi Mario, the fans worked fine - but it was the cooling that didn't work...

[chaconmorales]

Hi MattLomb,

Thank you for following up. I apologize for the misunderstanding or if it was not clear. However, based on the pictures and information provided, your system has more than one fan wire. The first stage is properly connected to the terminal and the Fan will definitely work, however the rest of the G wires are connected into inappropriate terminals. For this reason you should contact a Nest Pro to have your Nest Learning Thermostat installation reviewed. Incorrect installation settings can damage your system, your thermostat or both. Some systems that need to be installed by a Nest Pro include systems with G2, G3, GM, or GH wires. The wire for cooling is properly connected but the installation needs to be reviewed. 

Let me know if you need further assistance.

Best,

Mario