topic Re: Nest Gen 4 Fan control script AI in Home Automation

Nest Gen 4 Fan control script AI

Rodeng — Wed, 11 Feb 2026 23:21:24 GMT

I want my Nest thermostat Gen 4 to turn on the RTU fan on and off on a schedule. The Script Editor AI gave me a type: - type: device.command.ThermostatFanMode . However the Validator says this is not a valid or recognized type. The available options given included type: device.command.SetFanSpeed however fan speed control is not available on the RTU. Anyway would setting it to Max and off work the same as on/off? However Validate says device.command.SetFanSpeed is not accepted by this device.

Re: Nest Gen 4 Fan control script AI

Rodeng — Sun, 15 Feb 2026 21:05:42 GMT

@CoolingWizard

Re: Nest Gen 4 Fan control script AI

CoolingWizard — Mon, 16 Feb 2026 00:28:51 GMT

@Rodeng,

The command you are trying to use only works when the Nest Learning thermostat has been configured with a second or third fan speed wire. If the RTU does not have a 2 or 3-speed blower motor the command will not be recognized as valid command by the thermostat.
Now then the Google Home App does have the ability to set a FAN schedule to turn the blower fan on for say 15 minutes every 1 hour from say 12PM until 7PM.
Would something like this achieve what you want to do?

The command you are actually looking for is;

sdm.devices.commands.Fan.SetTimer timer.Mode [ON/OFF] , duration (in seconds)

sdm.devices.commands.Fan.SetTimer timer.Mode ON, 3600

this turns the blower fan on for 1-hour.

The Cooling Wizard

Re: Nest Gen 4 Fan control script AI

Rodeng — Mon, 16 Feb 2026 03:59:10 GMT

Thank you, however I know I can set the fan to run certain hours, but this is every day, no ability to choose which day. I need a script that Script editor will Validate to run the fan specific hours every Saturday and different hours every Sunday. Like my 40 year old Honeywell Chronotherm does.

@CoolingWizard

Re: Nest Gen 4 Fan control script AI

Rodeng — Mon, 16 Feb 2026 04:05:42 GMT

I should add, the Script editor AI came up with type device.command.FanMode which Validate wouldn't accept. Gemini came up with a similar FanControl, also rejected. I do not have multispeed HVAC fan motors.

@CoolingWizard

Re: Nest Gen 4 Fan control script AI

CoolingWizard — Mon, 16 Feb 2026 06:28:57 GMT

@Rodeng ,

You can. Create a script that can enquire the day and based on that day then use the script to turn the fan on for the number os seconds you want.

The Cooling Wizard

Re: Nest Gen 4 Fan control script AI

Rodeng — Mon, 16 Feb 2026 18:12:09 GMT

Thanks,

I understand your suggestion. I need a little more help though. What would the starter, condition and action script be for this instruction? Also I have not seen "smd" anywhere in the literature.

@CoolingWizard

Re: Nest Gen 4 Fan control script AI

CoolingWizard — Tue, 17 Feb 2026 05:31:07 GMT

@Rodeng ,

Have you taken any education classes in scripting? Or, are you just starting out as a newbie in coding?

What is your Project ID:

Are you registered to use the Google API?

The sdm pretext is an identifier:Smart Device Manager. When you analyze command
The Google Nest products have specific commands and traits as a smart device. You need to do proper research and understand what the commands available in the API are. You need this understanding before you ask an AI to generate your script. You can check you Sandbox for the device commands you are looking for.
To do what need to do will require advanced programing to determine the day-of-week then take action by executing your API specific commands for your device.

The Cooling Wizard

Re: Nest Gen 4 Fan control script AI

Rodeng — Wed, 18 Feb 2026 20:13:20 GMT

I replied earlier but this web page froze. I was directed to the Script Editor site and logically thought that the AI should be able to generate useful script but was mistaken. Even Gemini couldn't create a script that was acceptable. I noted that Google Nest does not even appear on the list of supported devices. https://developers.home.google.com/automations/supported-devices

In any case, I have given up trying to get fan control which should have been a basic app function and will be returning the thermostats to the store and will buy some Ecobees

@CoolingWizard