Going to revive this informative thread since I'm having an issue with mine.
My fan will not come on except for the very slow setting. Switching it to higher speeds has no effect. It does blow minimal air at the slow setting.
Does this same discussion/procedure apply to finding out what is wrong with mine? Thanks
* Bold added, see below.
Yes, except in the other thread you thought it was not coming on at all. So if you have low speed (or any other speed than high) but it turns off on the others you can skip some of the checks posted in #8 above. (see below)
* On the other hand if it stays on low as you turn the knob (as highlighted from you post) the knob may be cracked or damaged where it pushes into the speed switch shaft & the knob may not be actually turning the switch. In that case pull the knob & turn the shaft with pliers to see if you get the other 3 speeds. If it turns freely without getting the distinct detents for the other speeds the switch is probably bad. Test it further to verify. (see below)
Here is the test for the speed switch only from #8.
If no speeds, move to the speed switch. Check that 5 wire connector as you did for the 3 wire one. If you ground each of the 4 wires not including the dark green one (that goes to the mode switch) you should get each of the 4 speeds as long as the key is on. If yes, the speed switch is bad.