For some strange reason, the American version of the cabin fan seems to suffer badly from spark erosion
and corrosion build up a lot more than the Euro version of the 451, however, more reports are coming in.
You may find that the fan becomes temperamental. It may work fine one day, nothing the next and suddenly fix
itself again over night. Quite often, turning the power on to the fan and giving it (or the dashboard) a whack
will cause it to start working. Smashing the life out of the car isn't ideal though so you are better off fixing it.
This is a collaboration of information from WhiteNBlack08 from SCOA and pictures from Michael H.
Remove the blower motor and remove the screw from the rear.
Pull the motor from the housing to access the internals.
At the back of the motor is the motor controller, look closely at this part.
You will probably notice that the copper coloured segments (commutator) has burning or spark erosion over
the face. This is where sparking has occured over long periods of time. The sparking causes a build up of
non conductive corrosion which eventually stops any power getting to the motor to make it spin.
Use a fine emery paper to clean the copper faces. Visually check to make sure there is sufficient material left on
the carbon brushes that touch each side as the corrosion is very coarse and can wear down these connections.
Bob used an electrical contact cleaner and had good results. It is also less destructive to the commutator.
Reassemble the motor and get it a go. If it doesn't work, make sure the fuse is OK as the corrosion on the
commutator can increase electrical resistance which creates a spark gap which can cause too much power to
pass through the fuse which obviously can cause the fuse to burn, cutting the electrical connection to the fan.
Not really. The way you'd normally stop spark erosion is to apply a layer of non conductive grease like lithium or copper grease (non conductive at this voltage). The problem is that the motor spins which will flick the grease off and the carbon brushes will wipe the surface clear of grease in a few minutes.
Your only real options are to never use the fan (less than ideal) or use it as you would normally and
just fix it when it starts playing up. It's not a particularly hard thing to do so just fix it as required.
This confuses a lot of people. The fan stops working, they drive home and pull up outside their house
and the fan is still non functional. The next day they get in the car and suddenly it works fine.
What happens is, whilst the fan is working, it is arcing and causing spark errosion which creates a build
up of corrosion which in turn causes higher resistance. High resistance in an electrical joint causes heat.
Eventually the corrosion builds up so much that connection is lost and the fan stops working.
By this time, the commutator will be very hot so will have expanded slightly. You leave your car and the
connections cool back down to room temperature, the commutator contracts which can displace some
corrosion. With enough corrosion gone, you get a connection and the fan works again. For a while anyway.