Replace Honeywell vision pro TH8321 with nest learning thermostat U1 wire

[NestThermoRK]

Hello there,

I am trying to replace my Honeywell vision pro TH8321 with nest learning thermostat 3. I am able to map all the wires except one U1 orange color wire.

where to map this U1 orange color wire to Nest thermostat.

Please find the attached picture.

Thanks in advance!

[Markjosephp]

Hello NestThermoRK,

It's great that you're making the switch to a Nest Learning Thermostat. In most cases, the U1 wire on a Honeywell thermostat is used for HVAC accessories (i.e., humidifiers, dehumidifiers, and ventilators), the high fan speed in a multi-speed fan system, or the second to third stage of heating or cooling in a multistage HVAC system. However, the Nest Thermostat typically doesn't have a direct equivalent for this wire.

To address this, you have a couple of options:

• Before making any changes, it's a good idea to use the Nest Compatibility Checker. This tool can provide guidance on how to connect your specific wires and if any adjustments are needed.
• Do you have humidifiers, dehumidifiers, and ventilators? If so, it might be worth considering a professional installation. Incorrect setup, either due to miswiring or wrong software settings, can cause weird HVAC behavior and even damage your system.

Let us know if you have more questions.

Regards,
Mark