Is the oscillating mechanism engaged? Try to disengage it (if this model allows) and see if it makes a difference. I think the fan motor is just being overloaded and can't handle the extra load of the oscillating mechanism and that affects the main fan. It's probably dirty - perhaps some pet hair or some such wound on some rotating part.
What osciillating mechanism?  I can pull a button up  to make it stationary but the fan still operates the same.  It moves at a regular speed then slows down as if about toturn off then pick up again.  On low, it tends to do this more in the middle; on medium, it tends to do it more when it turns to the right and  on high, it tends to slow when it turns to the left.  I haven't had it on much since I noticed this.  Mostly just to check it out.  Will see if I can  find dust/pet hair.
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Pretty much every oscillating fan I've ever seen uses a shaded pole AC motor with tapped windings for speed control. That means that the speed of fan rotation is only controlled by the power the motors puts out, and that depends on which tap on the winding is, well, tapped. There is nothing electronic in the fan (unless this is some very high end model - can you post the part number?) that can control the speed in the fashion that you describe, which is why it is almost a guarantee the issue is mechanical and it is very often dust and hair that finds its way in and winds around any axle that's turning inside that fan.
There are parts of the oscillating mechanism gearbox that are always engaged to the motor and parts that you can disengage. If disengaging does not change the fan rotation behavior, specifically look for any problem - dirt, hair or perhaps even parts of the plastic body of the gear box, anything that does not belong - right around the motor shaft, the worm gear and the first gear engaged to the worm. You'll have to remove the cover of the fan and then remove another cover off of that plastic gear box that sits right behind the motor to get access to the worm gear.
will see what I can do- no thisis not a high end model=very inexpensive. Â Dust could be the problem. Â may have tog et help taking it apart- arthritic fingers don't always work. Â Is something- thank you for your help.
thanks-I suspect it is dust/dirt/pet hair-etc.
Hi, My pedestral fan rotates only in high speed that too only when the blade is removed. I changed the capacitor but no use. I disassembled the motor and put them back, but same issue. It can't take the load of blade. Motor hums. I need to rotate the hub for it to rotate even on high speed. At low speed it wont work even if I turn it. Can some one advice what could be the problem?
Thanks for the tip :) I was having the same problem. I flushed out the copper bearings with some WD40 to get all the black gunky dust out, dried it off and it did the trick!
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