When a range hood’s fan clearly runs — you can hear it, maybe even feel some airflow — but it’s not actually clearing smoke or steam, the cause is almost always downstream of the motor rather than the motor itself.
Backdraft Damper Stuck Closed
Most range hood ducting includes a one-way backdraft damper to keep outside air from entering when the hood is off. A damper that’s stuck partially closed will let the motor run normally while severely restricting actual airflow.
Duct Length and Bends Beyond Spec
Every blower has a maximum effective duct run, factoring in both length and the number of bends. A duct configuration installed beyond that spec will always underperform, even with a perfectly healthy motor.
A Disconnected or Crushed Duct Section
It sounds obvious, but a duct section that’s come loose or been crushed behind a cabinet or in the wall cavity is a genuinely common finding, especially after other work has been done nearby.
Getting a Real Answer
This kind of fault needs a hands-on check of the ducting itself, not just the hood unit — something our technicians inspect directly rather than assuming the motor is at fault.