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914World.com _ 914World Garage _ Fresh Air Fan Failure

Posted by: McMark Jun 3 2010, 11:31 AM

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.
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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.
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If you're rebuilding your air box, to install the new http://shop.914rubber.com/product.sc?productId=33&categoryId=1 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.
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Posted by: Tom Jun 3 2010, 11:43 AM

Thanks McMark, I will have to dig into this some day. My fresh air fan has never worked for me!
Tom

Posted by: detoxcowboy Jun 3 2010, 11:44 AM

Nice mark, very nice..

Posted by: realred914 Jun 3 2010, 12:06 PM

dont forget to lube that fan bearings too. the ones I found were very dried out.

I have added an aluminum bug screen under the coawl vents, above the fan to keep out the little debries . the factory had no screen early on, then added a very coarse screen, it is TOO COARSE!!! so add a bug screen on top., use teh metal screen, not nylon (you want it to last in the sun) and for pretty sake, spray paint it black before install. you should only use the bug screen on top of the factory screen, as the factory screen helps support the bug screen. if you need to upgrade to teh factory screen, you will need the upgraded rubber seal that retians teh factory screen. the early seal has no slot for the factory screen.

speaking of seals, the body to air box seal is very important , if it fails, rain and wash water will run down the outside of the air box, leading to a wet dash area, wet gas tank felts (rust!!) etc... so make sure yours seals.

some lubricated contact cleaner will help the fan slide switch to live longer once you cleaned it up!
while your at it, lube the wipers assembly.