mirousse

Though I could share this...

I've been having problems with the engine cooling fans since last summer. Either one fan or the two fans were not running. When running, they would modulate from high speed to low speed continuously. Also the engine flaps would cycle open and closed every 15-20 seconds.

The service manual diagnosis always led to the output stage (couldn't reach the 7 volts value and turning on the A/C would not trigger the fans).

I did the following:

1- Changed the output stage 4 transistors (25$ or so) and 2 capacitors (less than 5$).
2- Using the electrical diagram, tested all wire/connection/battery wires and cleaned all grounds

...still not working or at least not as they should.

Finally... I melted (re-soldered) all of the output stage circuit board solderings (eventhough they looked solid and new)...PROBLEM GONE...FANS WORKING FINE!!!

Michel
89 928 S4 ROW

Diehard914

Good timing with the post as I was in need of some fan info today after out whether hit 90 here in sunny Alabama. I have an 89 S4 and I am a fairly new owner still and need to understand the proper funciton of the fans. I have one fan that cycles on and off constantly when the temp reaches the middle of the gauge, maybe a hair higher than the middle but between the two main while lines. Yesterday my car was hovering at the top white line while in traffic. Does the second fan ever come on? My A/C is not fully up and running and I wondered if the second fan is tied to the A/C. Also, when I got to the second white line, should the fan still cycle even though the temp was not dropping to the middle of the gauge (basically just maintaining temp at that point.) Is my car functioning properly?

Please define "Fans working fine" so I know what I can expect.

Car details: Car has new Laso water pump and I used a hose to flush the radiator externally yesterday in hopes of lowering the temp range today. Louvers are not working to my knowledge and are stuck in the open position. I have no plastic underpan, it disintergrated when I took it off the first time. (I would expect this to allow more air flow especially allowing hot air behind the radiator to escape easier but who knows.)

Incidentally where is the output circuit board located and what does it look like so I can check my solder joints should I need too.

Thanks,
Diehard

Mrmerlin

thanks for the post info,
any chance you could post pictures of your work?

dr bob

The two fans work together, so having only one fan running at a time is an indication of problems. There are lots of threads on fan diagnosis, and the WSM has a diagnostic procedure but...


-- Make sure that both fans are actually plugged in. Your WP replacement included removing the fan console, so there's a very real possibility that one is not plugged back in correctly.

-- Check the connections at the battery. There are several 'extra' red wires attached to the positive terminals. Each fan uses one of those. Make sure the connections are clean (shiny) and the bolt is tight.

-- Fuses 28 and 29 are the fan fuses, one for each. Check the fuses, and also carefully inspect the fuse holder sections of the CE panel. Look for melting.

-- Try swapping the fan motor connections at the fan and see if the now-dormant motor actually runs. You can stimulate the controller by jumpering the two wires that attach to the intake temp switch on the top rear of the intake manifold. You may need to depress the hood switch to get them to run, per the owner's manual; mine don't need that.

-- The logic part of the controller lives under the cover next to the passenger's seat. The final output stages that the OP repaired are in the finned black housing on the front apron, leading edge of the hood area, right side (passenger side on US cars).

Diehard914

Thanks for the info Dr. Bob. I started with the easiest thing and checked the fuses, I was unaware they were on separate ones. The fuse on one fan is a 15 amp and it was blown and the other had a 25 amp which was good. I replaced the 15 amp with a 25 amp but will not try the car before posting here. When I got the car I used a guide I printed online, thought I found it linked to here somewhere, that showed all the proper fuse and relay placement for my 89 model year. I changed any fuses that were incorrect per the guide, there were not many but a few. I just found a printed version in the glove box and it shows one fan at 15 amp, the other at 25 amp so I know where I got it from. Is it correct for them to have different fuses or was this a misprint?

Thanks,
Diehard

dr bob

The fuse and relay chart shared by Dave Roberts and Wally Plumley on the 928 Specialists website shows the 15 and 25 Amp fuses for these cooling fan circuits. Meanwhile, the owner's manual, the factory in-car fuse and relay guide, and the workshop manual all show 30 Amp fuses in both positions. I'm not sure why the website list has differing recommendations from the factory manuals. In this case, I recommend following the WSM guidance on fuse sizes.

---

I have a copy of that 928 Specialists guide in the car, stuck in the CE panel cover with the factory CE fuses-and-relays guide. Next time I have the carpet lifted there, I'll pull them both out and compare them to see if there are other differences. I'm sure that Dave will quicly update his website after he reviews the lists.


Update 12-May-2011

The fuse and relay charts on the 928 Specialists website have been updated to match the WSM fuse ratings. For me, that means I'll be reprinting the updated version and replacing the copy in the car with the new copy.

Thanks to Wally and David for thier prompt response, and for this valuable service.

WallyP

The 1990 chart on our web site shows 30 amp fuses on both fans...

dr bob

Listed discrepancies are updated correctly as of 12-May-2011


Update 12-May-2011

The fuse and relay charts on the 928 Specialists website have been updated to match the WSM fuse ratings. For me, that means I'll be reprinting the updated version and replacing the copy in the car with the new copy.

Thanks to Wally and David for thier prompt response, and for this valuable service.

dr bob

Got my posters' year-models confused. OP's car is a '1989.

DIEHARD914's car is a 1990.


Discrepancies I listed above are ones I found for 1989 MY only. I did not look at other years.

Diehard914

Dr. Bob,
Funny enough you were right and I was wrong. I was thinking 90 degrees as in the weather yesterday and typed my year in wrong, I indeed own a 1989 S4 so you were very helpful, I now need to redo my fuse box according to the changes you listed!!!

Thanks, I will probably leave the 25 amp in till I get home from work, at least it will be safe and I will check all the fuses at home.

Thanks,

Diehard

fraggle

I can confirm both fans should mimic each other, and performance will be marginal to scary - possibly engine destroying in hot weather - if not addressed!!

Yes if you can please post pics of your solder work! If you can't maybe someone has a controller torn apart they can post shots of?

dr bob

Of course, you carefully logged which fuses you swapped when you did the initial change. So you can compare the old vs new vs WSM and see what's what. Do that before you change anything other than 28 and 29 for the radiator cooling fans anyway.

---

I did not go out and review what's actually installed in the fuse panel in my '89 car. Since I've still got all the original-capacity fuses in there I suppose I should compare with the WSM list to see if they agree before spouting off that something on DR's website isn't correct. Reality is that virtually all fuse panels will have the original-spec fuses installed. Unless someone has been messing with wiring or there's a fault someplace, there's generally no need to even change a fuse. Most fuses that get swapped for higher capacity are done because the cause of a standard fuse blowing isn't discovered by a frustrated owner. I have the luxury of having an unmolested car as far as electrical stuff, and the one change made to the car (HVAC control head relay) is well documented. So it's a good reference for how Hans and Fritz originally designed and built it.

---

Harbor Freight stores have a mini amp meter with a fuse-plug end on it. Less than $15 a week or two ago. Remove a fuse, plug in the meter, plug the pulled fuse into the meter socket to protect the circuit under test. Turn on your load and read the actual current passing through the fuse and holder. Reads up to 30 Amps, down to 100mA I think. It's still in the package out in the garage, since I --NEVER-- have electrical problems on my own car. So far. Knock on wood.

dr bob

Diehard,

Consider investing the relative pittance in Rennlist membership. That will let you add some signature information, like the year of your car and other stuff. It makes support a lot easier when we know what you have without asking. I'm sure this recommendation is in the "before your first post" thread someplace, but who reads that stuff before they pop a simple question? The few annual dollars to Rennlist helps keep the place running without the normal barrage of advertising and other junk.

Diehard914

I do remember the relative pattern of changes I had that night in that I noted how many were supposedly wrong right from the start (many of the first 8) then I saw them go correct for a bit then a few more changes at the end. I took into account everything else on the car wrong at first purchase (Aftermarket auto zone air cleaner, trunk release rigged up hanging out, right tunnel carpet hanging, phone cords stuffed under seat and carpeting, fog lamps that come on with high beams but not with the switch, no interior lamps working, and a battery cutoff to prevent draining, etc, etc) and decided the fuses were likely as messed with as the rest of the car and maybe putting them "right" might dig into my list of issues. I definitely reviewed the "before posting thread" and all the DIY tips and the many links cited, I think that is where I got the fuse panel map as well.

I like the idea of the harbor freight tool, very convienent way to double check that you are not overloading the fuse or that the fuse is properly chosen.

I am also considering the membership thing, first I want to make sure I survive the 928 experience, it was in doubt for a bit but things are sorting out now and I may just be around here a while if things keep improving. Must confess, I was ready to resell early in the experience.

Thanks,
Diehard

fraggle

I like the sound of that amp meter. My dvm only goes to 10A.

I have the original fuse/relay card for my '87 and it lists two 30A fuses for the fans. I would not expect the current demands to change by year, but who knows!