Cooling Fan Motor failure, with fusible link failure

[VetteMed]

I recently noticed that the A/C wasn't working well at slow vehicle speeds, and while I can accept that there's some reduced efficiency in such cases, yesterday the cooling was essentially nonexistent at a long stoplight.

Some troubleshooting this morning revealed that the secondary cooling fan is not operating. As per the FSM, checking for power at the large red power lead to the secondary relay, did NOT illuminate the test light.

I jumped the red power lead from the primary fan relay connector, to deliver 12v to the pink/black wire leading to the secondary fan, and it ran, but noisily and slowly. So, I think the secondary fan motor probably began to fail, was drawing too much current, and blew the fusible link.

I removed the battery, removed the nut off of the "jump starting terminal", and examined all of the fusible links. Here's what I found:



The FSM is vague about these fusible links, luckily the failure was visible. The two fan power fusible links are ganged together on one ring terminal. I'm going to replace both fan motors (they are both original), and both fusible links.

[scottfab]

The rubber on the wire looks brittle and corroded.
I'd expect there to be discoloration from high current.

[VetteMed]

Not true with fusible links, in my experience.

The insulation is very soft and flexible on this particular fusible link.

[scottfab]

Originally Posted by VetteMed

Not true with fusible links, in my experience.

The insulation is very soft and flexible on this particular fusible link.

Curious, I've never seen one fail that did not have melting and discoloration but I have seen failure due to corrosion from battery acid. The failure mechanism is this. The acid and/or vapor attacks the wire coating making it brittle. Then the acid continues in on the wire corroding it. Given some amount of flex on the corroded wire they eventually get to one strand or two that can't handle the current. They let loose and you have several other strands of wire making intermittent contact.

Here is but one example of what failure due to pure over current looks like.
http://www.eldorado-seville.com/file...sm_mg_8665.jpg

[Paul Workman]

Originally Posted by VetteMed

Not true with fusible links, in my experience.

The insulation is very soft and flexible on this particular fusible link.

Same here. Just a couple weeks ago my secondary fan took out the link. From the looks of it, the link itself was none worse for the wear - no discoloring or scorching - and still very flexible.

In doing a little research on fusible links I read where the insulation of fusible links is designed to withstand the heat of the wire melting without melting itself and possibly catching fire.

I replaced the link and the fan motor (with a new Bosch). I too took it out from the bottom. I was surprised at how easy a job it was.

P.

[VetteMed]

Summit and Jeg's both sell fusible link wire. I couldn't find any locally at any of the parts stores. The counter jockeys were trying to sell me a fuse holder, telling me it was the same thing. This occurred at 3 different stores. I hate that $hit.

[VetteMed]

Not sure why you are so skeptical.

There's over a dozen wires in that area -- none of the others have the slightest blemish.

The blown link has no sign of external damage to the insulation.

The melted ends of the copper wire strands are clearly not that way due to being dissolved by acid.

The fan motor is clearly not healthy, and therefore would easily draw too much current if the link were intact.

That all adds up quite simply, not sure why you doubt the validity of what I've stated.

[scottfab]

Originally Posted by VetteMed

Not sure why you are so skeptical.

There's over a dozen wires in that area -- none of the others have the slightest blemish.

The blown link has no sign of external damage to the insulation.

The melted ends of the copper wire strands are clearly not that way due to being dissolved by acid.

The fan motor is clearly not healthy, and therefore would easily draw too much current if the link were intact.

That all adds up quite simply, not sure why you doubt the validity of what I've stated.

Not sure why you think I doubt the validity of what you've said. I only state my experience with this area of our specific car (ZR1).
I am sure things are as you state and upon looking closely a the newest picture you post and compare it to the previous one I can see better the burn and melted parts. (lower image below) On the original I could not see it. (upper image below) There is a white powdery substance on the original (upper) that looked to me like corrosion but no sign of burn marks. Clearly on the bottom there are very noticeable burn marks and melted copper but no powdery substance. Anyway good luck with it. When mine failed I repaired the link and tighted up the fan. Obviouly a different failure mechanism.

[gbrtng]

Fusible links are usually 4 gauges smaller than the feed wire - meaning 20 GA link for 16 GA feed. I could not find the correct link gauge anywhere so I used a 25 amp slo-blow in-line fuse instead. My link blew when a small rock got caught between the fan hoop and the housing. Motor was OK and still in use after 10 years or so.

PS: I think fusible link wire uses a high temperature insulation to prevent a fire.

[Paul in VA]

Curious what fans you are going to use as replacements?