Article by: Gerry at PhoenixMotorsport
Article applies to: all e31 cars and most other BMW models.
OK, so over the last few weeks there have been a few posts on faulty AC fans so as I have done a few, I thought I would give some insight as to whats failing on these, why, and how you MIGHT be able to save the fan.
What we are looking at here are seized, stiff or very noisy fan motors. The same failure can cause blown fuses due to overloading.
Firstly, remove the fan assembly from under the triangle cover under the hood, ahead of the radiator by undoing the 3 x 8 mm nuts.
Break any? If so, things do not look good.
Now remove the fan from the motor my removing this outside circlip.
Next, undo the 3 x 8 mm nuts retaining the motor assembly to the shroud. These 3 here:
If you got all 3 undone you are doing well, on this one, 2 studs sheared off.
And this one needed a grinder to cut off the completely rounded nut.
IF you break off the studs it is not the end. As long as you grind them off flat and square, you can use a pillar drill to drill and tap a new 5mm hole and fit a small 5mm stud in to the case.
Caution: DO NOT go through the casing too far or you will hit the motor.
Now, to take the motor apart, the casing is just peened over around the edge in about 6 places. I use a Dremel to remove both the peening, and the corrosion around the joint.
I also cut a small slot in 1 position so I can tap the face plate from behind to loosen it up.
Using 2 screwdrivers under the flange, lift out the rotor.
CAUTION: the rotor is held in pretty tightly just by magnetism, do not get your fingers trapped between the rotor plate and the stator housing. This rotor is in good condition.
Which is more than can be said of the stator:
Generally what happens is rust builds up behind the magnets and pushes them off the casing. They then wedge the rotor and seize the motor, or rub against the rotor and overheat it or increase the current draw that blows the fuse.
Here you can clearly see the excessive corrosion that pushed this magnet off, which then broke up inside the motor. I have found some where the magnet is just coming adrift and the case can be cleaned and the magnet glued back in position.
Whilst apart, you can check the condition of the motor brushes and rotor bearing.
At this point you can decide whether or not a repair is practical.
On re-assembly, I grease the bearing and assemble the motor, but do not peen it over as the shock could dislodge a magnet.
I epoxied the case back together and use stainless nuts and washers eliminate the risk of corrosion should the motor need to come apart again.