Saving the Stock Aux Fan

Over time, carbon builds up in the motor causing several problems. Sometimes the electric fan starts running erratically, like it does not always want to start. Sometimes, when you turn them by hand, you will feel them "cog". By this I mean that it feels like it is going past notches. A DC motor should turn smoothly.

Here is how to reclaim a 97+ Fan Motor.
1. Remove the C-Clip and metal spacer securing the blade to the motor.
2. Remove the blade from the shaft. Tap the motor shaft LIGHTLY to get it off. DO NOT PRY ON THE BLADES, THEY WILL SHATTER!!!!!!
3. Remove the three screw securing the motor to the shroud.
4. There are several tabs that are bent down holding the backing plate. Gently pry these up to release the backing plate.
5. Blow out the built up carbon dust from the inside of the motor. As the motor operates, the brushes wear depositing carbon everywhere. This shorts the segments causing the "Cog" feel.
6. Gently clean between the commutator segments to remove the carbon. A very small scribe works well.
7. Reattach the backing plate by gently bending the tabs back into place.
8. Reattach motor to shroud.
9. Reattach blade.
10. Test.

This is a, usually, one time repair as the tabs holding the back plate on tend to snap off with repeated bendings as they are just thin sheet steel. It is also possible to just buy the motor by itself. Google the part number that is printed on the motor. It is a Bosch Part.

You realize, of course, that now that you have posted this, it will be the next thing I have to fix on the kid's 97? JK Good to know.

the "cog" as you call it is the magnetic field from the windings in the motor. It's the North and South poles of the field. As you push a little you get more resistance, then as you clear you get propulsion

ehall said:

the "cog" as you call it is the magnetic field from the windings in the motor. It's the North and South poles of the field. As you push a little you get more resistance, then as you clear you get propulsion

Click to expand...

Quite right.

Unless the DC motor in question is a Stepper Motor, it should turn freely. I figure there are more mechanical folk here than EEs so I described how the motor feels in mechanical terms.

Once the commutator is no longer shorted by the carbon dust, the motor will, once again, turn freely. Due to the shorting, a slight voltage is being induced in the armature windings which causes a magnetic field to be generated that, in turn, interacts with the permanent magnets.

I have, in the past, added a touch of lubricant to the motor bushings.

Beats buying a new one...

May be retired, but my EE is still good, I think...

I took mine apart and cleaned the commutator and other debris. I was inspecting the brushes, I noticed that the braided copper wire on one of the brushes was actually severed. Is it possible to replace the one brush? They appear to be "spot welded (soldered) to the backing plate.

Difficult to do at best. The best idea here would be to replace the motor. Google the part number that is painted (white paint) on the motor. Number is located near the mounting points and is applied by ink jet so has a dot matrix look to it. Bosch part.

I have seen non-Bosch motors go for as little as $25. Not sure I would trust the Cheap Chinese part... Four Seasons make a replacement motor but they start at $112 and go up depending on the quality. Makes a pick from the JY look really good. The U-Pull-&-Pay here in the Springs gets $14.99 (+ the Govenor's share...) for a complete fan. Worth looking into.

Thanks for the advise. The nearest bone yard is 100 miles away for me. I ended up buying a Chinese fan but will be looking for a backup. Not sure the $112 motor isn't foreign made as well???