Fan running even after Nest Thermostat Gen 4 is off. Turns off when removed from base after 3min

[Karthikrao]

Fan is running continuously even after Nest Thermostat Gen 4 Cool/Heat is turned off. Unit is a heat pump.

Wiring and everything seems good. 

Only option for the fan to turn off is to remove the thermostat from the base. Once that is done, Fan will turn off after 2-3 min

I am tired on this..Any pointers?

[CoolingWizard]

@Karthikrao ,

this is not the thermostat that’s causing this to happen. Many more high-efficiency systems run the fan after the compressor turns off to get the last bit of cooling capacity left in the refrigerant as it expands inside the evaporator coil. Typically this runs between three and five minutes after the compressor turns off. This is controlled by the actual control board in the air handler and has nothing to do with the actual thermostat.

the best way to check. This is to get a volt on meter and see if the thermostat is calling for the fan to be running at the air handler by checking the voltage. It’s running between the C wire on the air handler and the G wire on the air handler. If you see 24 V, the thermostat is making the call for the fan. if there is no voltage shown then it’s the control board that is doing this. 

The Cooling Wizard

[Karthikrao]

@CoolingWizard Thanks for getting back. I asked my HVAC technician and he is pointing towards the Thermostat. Isn't the FAN needs to turn on and off based on HEAT/COOL settings? There is no ON/OFF for the fan. I an lost on how to address this.

[CoolingWizard]

@Karthikrao ,

The only fan parameter is with heating setup.  You can have the Integrated Furnace Controller control the fan in heating, this is the normal, or have the Nest Thermostat control blower fan during heating.  The Thermostat typically does not control the blower fan during heating unless it is a heat pump.  Did your HVAC guy actually measure the voltage on G and Common to verify if the call for fan was coming from the thermostat? In heat pump systems yes indeed the thermostat does control the blower fan 100% of the time.  

The Cooling Wizard