When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
The common cooling fan failure mode returned today (cycling on and off like a Cessna with engine trouble), after being cured for almost two years. The good news is it seems to be the same cause (poor fuse contacts) - but a bit more troubling evidence of heat.
The previous fix: Deoxit in the fuse sockets and new fuses. At the time I noted scorched upper spade sockets. Interpreted this as evidence of oxidation causing greater resistance and resulting in a history of getting too hot. (Old fans may also be drawing more current but still beneath the threshold of blowing the fuses).
I've had no problems with the fans since the simple fix above. However, I've recently got the AC working again with a recharge. I started to use it in the recent hot weather....and this makes the fans run all the time....apparently resulting in the fuses getting hot and staying hot...and melting...
I've pulled the fuses occasionally and they've been fine. But that was before I started using the AC.
Here are the sockets... (I pulled the 15A fog lights fuse on the far right to compare)
So here's what I think has happened... oxidation over the decades degraded the fuse panel contacts...heat burned and deformed the contacts, further increasing resistance....more tendency to heat up. I've read a few posts about old fan motors drawing more amps as they age. This could be a contributing factor (but one that, too, is not significant until the fans are running all the time - typically with the AC on).
So, I've sprayed some Deoxit in the sockets. I'll put in new 30A fuses tomorrow and see what happens. If the fans return to normal function I'll consider it a temporary fix.
The permanent fix at least includes new fuse sockets. I need some suggestions on how to accomplish this. Can the blocks of 5 fuses be replaced (not the entire panel)?
Last edited by Captain_Slow; 10-08-2016 at 10:29 PM.
You can replace the blocks of 5 fuse holders, you can also replace individual fuse contacts within a 5 fuse block (though that doesn't help if the plastic is badly heat damaged - and won't look good even if it is only slightly charred).
Anyway an important note to all. Fuse blocks are not interchangeable - they are numbered by fuse location (not easy to see) and even by location they vary by year. Internal to the fuse blocks (not visible) there are sometimes shorting bars on the input sides of the fuses (shorting various inputs). This is why if you look on the rear of the panel - it will appear some fuses have no input connections. You can use the same numbered fuse block from the same numbered CE panel or - otherwise you must check the configurations - you can test electrically - or open up the 5 fuse block and assess visually. Shorted terminal blocks can be separated (cut/file). If you need a shorted block and don't have one that is more problematic.
On an '88 the fuse block for #26-#30 is a partially shorted block you need 26 & 27 inputs shorted and 28-30 not shorted. You must get the right kind of block.
This is entirely a poor fuse connection issue - it has nothing to do with the fans condition. More intensive usage will cause faster degradation as it allows more heat build up - but it is not a cause.
I had this problem on one of my cars... fan loses power and the other cycling on and off, with associated scorching on the fuse block.
On removal of the CE panel and removal of the fuse holder I noticed that the fuse leafs were somewhat loose. Bending these back for a tight fuse fit fixed the problem, going on a couple years now without recurrence.
I suspect oxidation can create a hot spot and maybe the leafs can loosen up due to that. Another reason to periodically remove and reinsert fuses, or clean/inspect the CE panel if never done.
Earlier this morning I made a trip to NAPA and picked up a kit of Bussmann fuses. Deoxit and new fuses has returned the fans to normal operation. However, it certainly looks like I need to try Mark's method of refurbishing the contacts in the fuse holders. If that doesn't work I'll have to replace them (just the holders if not the entire block of 5). A good set of used would be fine.
This problem began on the PO's watch. He had several used fan controllers (the one's beside the passenger seat and perhaps a final stage "amp" as well). None of them solved the problem and I could tell he was done with trying to fix it. I went down that same rabbit hole without considering fuse sockets had become the source of the trouble due to the oxidation and increased resistance. I checked the fuses as soon as got the car home, but I did not clean the sockets with Deoxit and put in new fuses - had I done so the root of the fan problem would have been found before trying yet another pair of controllers. I now have working spares for the final stage (rebuilt by Theo) and controller next to the passenger seat.
Alan - thanks for answering the question about replacing just the fuse blocks, and providing the critical info on getting the proper blocks. I can see this going wrong for many who are unaware. Thanks for clarifying the relationship between the running fans and the heating - not a cause, but still relevant.
Betrand - thanks for providing all the related threads. Servicing these panels really is important preventative maintenance. Unfortunately, the fuse sockets 28 and 29 were already a bit crispy when I bought the car. No worries, the proper repair is known and the fan mystery solved.
Alan,
These links were very helpful. It sounds like I should ask 928 Intl for the block from a panel out of a "88 (e.g. "Fuse holder block 26-30 out of a 1988 S4"). Or, should I also refer to some unique identifier on the block itself?
Blocks containing these high current circuits are likely to experience this problem (again, realizing it's the degraded fuse connections that are causing the problem), leading to short supply over time. Are there other blocks in the 1988 panel (or other years) that have the majority of fuses connected - making it possible to cut the internal copper bridges apart for multiple repair situations? If yes, then I think I'll buy several for spares that can be modified for use anywhere in the panel.
Thank you again for your invaluable knowledge and support.
For an '88 you could get any other Blocks 1-5, 6-10, 11-15, 16-20, 21-25, 31-35, 36-40 or 41-45 and have at least 2 ganged input holders - however none of the others have the exact configuration you need - so all will need adaptation.
An '87 or '89 or a '91-'95 will work perfectly for you for #26-30 also - and the other blocks of those years are similarly useful for reconfiguration.
'85, '86 and '90 don't work for you (though their alternate holders can generally be used for reconfiguration supplies somewhat similarly - get a few blocks).
These #26-30 fuse blocks are actually amongst the ones that change the least Year to Year (but they do still change).
The numbered blocks are just generic shells - there is no way to know by their Porsche ID what year they go with (e.g. what internal configuration they have).
This is timely. I just spent the evening diagnosing a battery drain issue and while I was pulling the fuses I noticed that my rad fan fuses were in the process of melting. They were actually worse than yours, but the plastic on the fuse blocks didn't seem to have melted yet. I sprayed the fuse holder with a bunch of Deoxit and replaced the fuses, but I'll have to keep an eye on it to make sure that it doesn't reoccur. I have another melted fuse though (my HVAC blower) which actually did melt the fuse holder so I'll have to get a new block. Fun times!
07-10-2016, 12:14 AM
S4 Cooling Fans: melted fuses and burned sockets
