928porschemangreg

On my 89, when the second fan quit running (Which caused an overheat on a hot day like today) I found the wires from the fan harness and a taped repair there were toast. Replaced wires to both fans. (Or of course one of the fuses would be an obvious issue) There are 2, 30 Amp fuses and they can melt/have bad contact, etc.

MainePorsche

Does the fan spin freely, or better yet, like the other one when you give it a flick ? Could be the bearing or other motor internals. On my car, when one fan failed it caused such resistance in the whole circuit both fuses blew.
Check the physical state of the wires.
After you do these two, then check the two fuses.
If the fan, you will note the asymmetry in its lack of free motion.
If the wires have a break, it will speak for itself.
If both the above are 'normal' press the AC button and see what your voltage is at each of the fan connectors.
See what you have and come on back.

Captain_Slow

Robert - time for you to read the threads posted by myself and MainePorsche over the past 10 days or so (both dealing with S4 fan issues). My passenger side fan doesn't come on either. Likely your final stage controller (looks like a small amp - but it isn't - seen on front apron after you open the hood). Rebuilding these should become a clinic...they are dropping like flies.

Confirm your passenger side fan is working by switching the fan connections. If pass fan doesn't work when powered by left fan connection - then the fan is bad, perhaps not the final stage (but a failing fan could fry that channel of the final stage...but too soon to talk about this). Is your left fan running on full power and cycling on and off, while the right fan does nothing?

CT Rob

I haven't swapped cables yet, but I did confirm the fuses are fine, and the fans can both be turned by hand. The one fan appears to be doing all the work.

I am running through the diagnostic on pages 19-22 to 19-26 of the factory shop manual.

MainePorsche

Yes, that is the thing to do.
Report back the specific findings at the various pin combinations.

Alan

No - the fans still run when the hood is open if the engine is running. The hood switch only disables the fan 'after-running' (the auto cooldown mode with ignition off) - this only triggers if the intake is very hot.

Alan

Alan

On an S4+ it is always both fans together.

Same just with AC on - it does turn off during starting (for load reduction), however it would be better if it didn't come on until after starting (its a quite large current). Good reason not to sit with engine off, accessories on and AC turned on...

It should so the fan/controller have an issue - plenty of threads (even recent) on this...

Alan

CT Rob

Looks like the control unit and amplifier pass the tests, and the A/C switch does turn on the one working fan. How do those connectors disconnect from the fans? I don't want to risk breaking anything.

I am thinking it's either the fan motor, or the wires leading up to it.

MainePorsche

You can reach them from the top. Each fan has a 2 pin connector and they sit at a slight angle. Just rock back and forth, and they'll come off. You may, for confirmation of your work, check the voltages at each connector when AC button pushed. Careful, and don't let DVM wires get into the fans.
Still have to get under and give a good inspect of the wires.
Good sleuthing.

CT Rob

There's voltage (4-6V DC) at the plug with the ignition on and the A/C switch engaged, but the motor isn't turning, so it looks like I need a fan motor.

MainePorsche

WSM says there should be 7v at low output, so you're in the ball park. Maybe some Deoxit at the various connections will be helpful.
I'd unplug the fuse for that fan - when I had same issue the resistance caused the other fan fuse to blow.
Well there ya' go - an answer.
Good job.

dr bob

Some fan basics for S4+ cars:

Each fan has a dedicated power feed connected at the battery positive terminal. There are several smaller connections to the positive post, including these fans, the fuel pump, and the fuel injectors. Make sure that those wires and connnections are clean and tight. More than a few folks have had one or both fans "fail" due to loose connections at those smaller wires at the battery positive.

Each fan motor has a dedcated fuse in the CE panel. On my '89, fuses 28 and 29. You can test for voltage at both sides of those fuses. You should see battery voltage on both sides of each fuse. Check there when the fan is supposed to be running to see if there's a problem between the battery and the fuses and holders in the CE panel. Voltage on one side of a fuse but none on the other means a fuse has blown. You'll need a pretty small-tipped probe on the meter to poke iinto the opennings on those fuses, and you measurement is with chassis ground as reference.

CT Rob

I am guessing that my voltage readings would go up a little if the engine were running, rather than just going on battery power. As everything else appears to be in good working order, and it is acting more like a break than a short, I am hoping that just changing out the fan will remedy the situation.

Now for the hard part -- waiting for the fan to arrive in the mail.

Thanks for your help!

MainePorsche

No Rob, the PITA part is pulling the shroud in our cars. Sorry to be the harbinger of PITA news.
Best Wishes,
Craig

CT Rob

In that case, it sounds like a job for my local 928 mechanic.