MainePorsche

You know Alan, in thinking about it the voltages were probably 7.2 and 9.2 while running. These would be more along the line of being realistic. I had carpets folded up (access to CE) - had side panel off for access to controller on top of plastic over the seat - DVM in the shadows. I must have misread.

MainePorsche

Just thought I'd comment on an interesting finding today.
Hot humid day up here - AC on - slow stop and go driving - engine never got 'overly hot'.
When I pulled into the garage turned the AC off - the one fan still going - but when I turned the ignition off the fan would not stop - I stood there for at least two minutes and still on - I was going to take an action, and when I opened the hood it stopped - odd never did that before. Usually if the car was hot I would have ignition switched so fan would run for a final cool down before I walked away.

Have a plan for the fix that I posted in Jon's 'S4 Fan Fun...' thread.
Will update as the materials arrive and I install.

Bertrand Daoust

Not 100% sure but I think that's normal.

The engine was probably warm enough that it requires the fans - 1 in your case - to continue working (after the engine's off) until the engine gets cooler. This is the sensor at the back and on top of the intake that controls this.
As soon as you open the hood, it stops by itself. That's a security device.

NC928S4

I agree. Press the "Hood/Bonnet" contact switch and the fans should continue running. Depressing the switch lets you observe Fan behavior as she warms up and adapts when AC gets turned on.

I've observed that from a cold engine start with AC ON both Fans do not kick on until engines reaches normal operating temp.

Captain_Slow

I wish my one working fan would continue to run when I turn off the engine. Maybe it's not getting hot enough, or I need a new sensor on the intake (although I won't need it because the Delta Controls controller will run the fans for a period after shutdown. I'd still like to know if the sensor is bad). When I pull the leads off the sensor and connect them, with hood open and hood switch pressed, the one working fan will run.

Now that the weather is warmer I pull into the garage after a drive, pop open the hood, and place a fan on high blowing directly into the mouth.

MainePorsche

Fellows, I thought so too but I never had them run for any period when ignition OFF and key out. I would always let it fan run with key in position 1 for about 30 secs, then turn it OFF and was done. I've never seen my car run the fans with ignition OFF. I knew the bonnet switch was a safety device, and actually turned fan ON & OFF for the 2 mins by depressing the bonnet button.
I just thought it was odd for I'd never seen this behavior before - maybe I'm just running a little hotter now - then it maybe another issue for my gauge is not reflecting this - another thing to look into. This car causes one to be forever skeptical and on guard.

MainePorsche

Jon,
At least you know the circuit if OK and you haven't lost continuity of a wire in Yenemsvelt, as my Grandmother would say. Tracking, finding, and repairing a wire there is never an easy task.
Before I would go to an new sensor I would clean the contacts first, then get some Deoxit 100 on it and see what you have.

TheoJ

hi,
the fan power amp is a rather clever device. Well made by Hella. But they do fail. A typical phenomena is that one fan runs full power (like a Chessna) and the other one is off. And sometimes the problem shifts to the other fan. The system mis-interprets that one fan has failed.

Power supply (fuses, wiring) and the actual fan can cause this besides the power stage and the fan controller box next to the pass.side seat. To quickly make sure the main power and the fans are ok, try this:
Troubleshooting:
Step 1: check if the fan itself is ok. Do this: unplug the connector at the power stage. The connector has numbers on it. Take a decent wire to make a jumper wire. Avoid risk on short circuits. Carefully (!!!!, this is 12v but maybe 10 Amps) connect Pin 1 to pin 8 to power up the Fan1. Fan will run max power, so watch out for anything in that area like wires. Next connect Pin 4 to pin 5. The Fan2 will run. If that works, you verified that the fans are operational, and the problem moves to the power stage or controller box.

Step 2: look at the connectors at the pass side Controller box. Two flat connectors will be there. Find in connector 1 wires 6 and 8 (6=blue and 8=green) and on connector 2 wire 7 (grey). I think the wire 7 is the on signal, a Ux signal to the power stage to send electronics power to the fan power stage (not the fan main power). The other two are controller/return signals. Check voltage on wire 7. You should see a 9v or similar when you activate the AC. The Sign 1 and 2, wire 6 and 8, should carry a voltage. If no voltage is there on one and the other has 12v, I’d suspect the power stage. But I was also puzzled once that it turned out to be the controller itself, blocking the signal….

If you see 19v at a running fan, you might be looking at static noise on the 12v. Or there is something very wrong with your DVM/Car... can't think of any reason why you should see 19v.

regards
Theo Jenniskens
1992 928 GTS midnight blue. (exclusive version)

Captain_Slow

Theo -
Thanks for this additional fan testing procedure. Is it possible that over time, as perhaps one fan has degraded more than the other, that more than 26A of current passes through the FETs for that fan channel and fries the FETs? (noting that the fan main power fuses are 30A). In other words, is it possible that an aged and worn fan can produce a situation where the 26A FETs are protecting the 30A fuse? My hunch is that new fans probably never draw near 26A so that this problem doesn't arise until at least one fan had degraded to a point where it may draw more than 26A (perhaps while starting the fan?). Could one repair a final stage (new FETs at least) and have the same fan channel fail (quickly if replacement FETs have similar amp rating as the originals, or perhaps taking a bit longer if the replacements are say 50A+ FETs). I guess, ultimately, what I'm saying is....should the inoperative fan be rebuilt if it's possible its condition caused the failure of its respective channel in the final stage controller?

Aside from spinning each fan by hand to feel relative resistance to turning, would it also be possible to evaluate fan condition by observing how fast the fans spin relative to each other when jumped as you describe above? (degraded fan spinning slower and drawing more current?)

My test results of the controller by the seat were all normal as stated in the WSM (and as you describe above...about 9V at pin 7 in connector 2, and battery voltage at the pins in connector 1.

TheoJ

Hi Jon,
the original FET's are pretty good, there are two FETs covering one fan. 4 in total. They can provide power for teh fans with no problems. 17Amps in nromal operation when not dragging or so, about 20 amps when starting and catching up speed. If you see one fan running faster than the other you may be on to something. Putting full power on them should show them running similar. If the bearings are gone you may feel this by turning with your hand.
Yes, if the fan has fried wiring inside the motor, the FET's will break down unless the fuse cuts power. FETs do not damage very quickly, but they do have internal components that can't handle peaks of 50 amps before the fuse blows (fuses are rather slow). What I'm saying is: if you replace the FETs because of a malfunction you better replace all 4, and check the fan motors for they may have caused this.
Just for your information: it is definitely not always a FET stage that causes the problems in the power stage. There is more to it. And the controller does turn one fan off if it thinks it failed. Could very well be that the fan is fine though. Put power on it and check for yourself, check amps is possible. Compare power draw on both fans. Similar? Then you'd probably be ok there.
regards
Theo Jenniskens
1992 928 GTS midnight blue. (exclusive version)

Captain_Slow

Theo -
Thanks for this excellent information. I noted the inoperative right fan would run a bit slower when connected to the left fan's connector. The left fan works fine and runs very strong and loud. For a moment I thought by connecting the left connector to the right fan, I would possibly witness the failure of the left channel.

I'm going to try your jumper test to run each fan off 12V "unfiltered" by the final stage. If I sense one is slower than the other I might try some white paint on a fan blade (both fans) and an adjustable strobe light to try to quantify the frequency difference.

Captain_Slow

Jumped pins (actually sockets in the final stage cable connector) #1 and 8. Driver's side fan ran on full power. Did the same for sockets #4 and 5. Passenger side fan ran on full power. Again, it seemed like the driver's side fan ran stronger and louder, but not much. The passenger fan is buried under the top radiator hose and (on my car) the alarm horn. I think sound from the passenger fan is just a bit muffled. Grabbing and moving a blade back and forth, or flicking them to spin them, both move freely and feel the same.

I'm going to get the DC Controller so that I have no-compromise backup system I can use indefinitely while sorting out the final stage and possibly temp sensors in the original system.

My biggest concern remains getting the final stage cover back on, and sealed as well as from the factory. The factory method of attaching the bottom plate to the aluminum case/heat sink does not look like the plate was to be removed for service and replaced. I know Greg Brown has figured out his own proprietary method - and he also stated that this was one of his biggest concerns.

BTW: the fans ran when jumpered without turning the key. So these sockets are being fed right off the battery. The final stage is handling the pulse-width modulation of the battery voltage based on the square signal it gets from the controller by the seat....which is determining duration of the square signal based on all those temp sensor inputs. I think.

Alan

The fans are designed to run for a while when the ignition is turned off and the intake is very hot - this does not mean the car was running overly hot - just that it is fuilly heat soaked. e.g. freeway speeds then pull off to rest area & shutdown... In many climates meeting these conditions is quite rare - in Phoenix this is a daily occurrence in mid summer after a long enough drive (say > 20 mins).

The fans may run when the engine is running - even with the hood open, but when the ignition is off the fans will never run while the hood is open (via the hood switch). This is to prevent unexpected fan and hand contact - it's assumed only an idiot would put his hands near the fans when the engine is actually running.

(Likely plenty of idiots have already tested this theory... )

So what you observed was completely normal.

Alan

MainePorsche

Just taking a break from the tedious task of running wiring into/through our engine compartment, and the crimping while in awkward positions. Today is dc controller install to replace the down amplifier and renew my fan control system. I will start a new thread with an appropriate title so it can be searched later on.

MainePorsche

Finished for today. To many interruptions. Will finish tomorrow and start the thread describing what was done. Will try to get some pics with it. Unit in and ready to function. Will wire in the AC activation switch, the torque converter temp sensor, intake temp sensor, high pressure refrigerant temp switch - this will be easy as will be done at the passenger seat controller - car is up so I can sit while addressing it.