Google Nest
Fan Control Circuit Failure
Nest thermostat does not turn on the fan in Fan Only mode
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
G wire not connected or loose, G terminal miswired at furnace, Failed fan relay on control board, Blower motor failure
How to Fix / Troubleshooting
Safety first: Turn off furnace/air handler power before accessing wiring.
- Test Fan Only mode: On the Nest, set the fan to run manually and listen for blower operation.
- Inspect G wiring: Ensure the G wire is firmly connected at the Nest base and at the furnace G terminal.
- Bypass test (advanced): With power on and access panel in place, a technician can jumper R to G at the furnace terminal strip. If the fan does not start, the relay or motor circuit is likely faulty.
Fan relay or blower motor replacement should be performed by a qualified HVAC technician.
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Repair Difficulty
Hard
4/5
Required Part
Nest Thermostat Base (G terminal), Furnace Control Board, Blower Motor
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