Just because your bathroom exhaust fan is running,
Doesn’t mean it is working properly.
I was working on an exhaust fan in a bathroom today, it was filthy, noisy, and it didn’t seem to be moving the air through the vent. I decided to open it up and change the motor, and clean up the housing. After opening the cover and removing the fan motor, I noticed the back draft damper was stuck solid in the closed position.
(The photo is taken from inside the original fan.)
No air was flowing through the bathroom exhaust vent!
That explains the lack of air flow. It probably could have been cleaned up and reused but I felt a new fan just made more sense in this situation. Now when the bathroom exhaust fan runs, the air flows through to the vent as it should.
(The is a photo of a bathroom fan showing how the damper should move)