Carrier VFD fan coil unit

[BW4]

Existing Nest Learning T-stat connected to wi-fi. New carrier system installed a few days ago, 38MURAQ condenser/compressor (low ambient) with 40MUAAQ fan coil with VFD.  Heat pump wire connected to the “B” terminal.

Q1: Fan seems to only run at one speed. Is Nest compatible with VFDs, ie. under what conditions and how will it control fan speed?

Q2: If Nest company pushes out a software upgrade, will it change my heat pump back to an “O” terminal connection?

 Thanks

[zoeuvre]

Hi BW4, 

Thanks for reaching out to us. The Nest Learning Thermostat may not directly control the variable frequency drive (VFD) of your fan coil unit. The Nest Thermostat typically controls the HVAC system based on the inputs it receives from the connected wires. The fan speed control of your system may be managed by the equipment itself or through separate controls specific to the VFD. It is recommended to consult the user manual or contact the manufacturer of your fan coil unit for information on how to control and adjust the fan speed in conjunction with your Nest Thermostat.

Software upgrades from Nest may introduce new features or improvements to the thermostat's functionality. However, software updates typically do not modify the wiring configuration or change the terminal assignments on the thermostat itself. If your system is currently wired with the "B" terminal for the heat pump, it is unlikely that a software update alone would change it to an "O" terminal connection. 

Let us know if that helps.

Best,

Zoe

[BW4]

Thanks. I read that the Nest will only  support one speed. Decided against the Ecobee because the Nest is learning tstat . The Carrier seems to be running fine and speeds have varied, just not sure if the VFD functionality is fully enabled. Thanks for the “B” terminal info.

[zoeuvre]

Hi there, 

We're sad to see you go, and thank you for taking the time to show interest in our Nest Thermostat. We're always here to help if you ever change your mind.

Regards,

Zoe

[BW4]

Sorry if I was confusing. I am keeping the Nest and it works well with my new heat pump. Thanks.

[zoeuvre]

Hello BW4, 

No worries! If you come across other information you'd like to pass along or have more questions, feel free to create a new post.

All the best,

Zoe