Fresh Air Fan Failure, pictures Options

[McMark]

A great number of cars that I've seen have fresh air fans that don't work. They can get clogged with leaves, and a subjected to rust and corrosion just like anything else. It's not really any big surprise that some motors are beyond repair, but I've never dug deep enough to find definitive evidence. Until now.

The motor had bunches of leaves and lots of corrosion keeping the motor from turning. When power is applied to the wiring under these conditions, everything starts heating up massively and things start melting. The most obvious place this heat build up is seen is on the in-cabin switch. It's not uncommon for the plastic surrounding the wiring contact to be melted. In the picture below, you can see that the plastic around the brass contact in the middle is melted.


While the melting on the in-cabin switch can often be repaired by carefully removing the melted plastic, it's also possible to melt the internal parts of the fan motor itself. These pictures below are of the brushes in the blower motor. You can see how badly melted the brush housings are. Nothing is going to fix this damage. The motor is toast.




If you're rebuilding your air box, to install the new 914Rubber fan box seals for example, you can check the brushes for damage by looking closely at them with a flashlight. This picture shows roughly where the brushes are, and you can peek around that area with a flashlight and see if you see any signs of melt damage. You can also pop off the clip (arrowed), be careful of the spring behind, and check that the brushes move in their bore easily. I revived the fan pictured, by removing the clips and springs and applying heavy pressure on the back of the brushes while turning the fan by hand to help clean off some of the corrosion. It turned right on after that, whereas if didn't work at all before.