danglerb

What is the input to the S4 fan controller like, logic from a brain, or analog from a sensor?

dr bob

There's a separate 'smart box' that reads the radiator temp sensor, the freon pressure, AT fluid temp, AC run status, engine run status, the hood switch, and the intake manifold switch. It outputs discrete step signals to the front flap controller, and something to the final stages module to tell it target fan speeds. I don't have the WSM handy with the test procedure. But the final stages module in front does not read analog or discrete sensors/switches directly.

Mark Anderson

I'm up for 10

fraggle

The smart box that Dr Bob is referring to is located next to the passenger seat in the same enclosure as the radio amp.

yardpro

depending on cost i would be up for one as well...

i have been putting off my hvac R&R... i need to get my but on the stick

LeRox

This is wonderful news and when can we expect working examples to be distributed. I have a rebuild scheduled and may put it off until next spring....

jleidel

Dr. Bob, thanks for getting those measurements. Apologies all for the few days of silence. Our lab crew has been chasing down some circuit tuning wackiness on our forthcoming product line. [for those with EE backgrounds, debugging a 24-layer board with high speed serial links can be challenging]

At any rate, I'll get these values into the model and we'll nail down a final circuit schematic. The initial parts list doesn't look hairy at all. I have a good idea what sort of volume we're dealing with now. As soon as I have a reasonable idea of what the board fab will require, I'll try to post some rough cost estimates with a few options.

Thanks again all.

ALKada

John,
Any updates? I know you were in the process of moving recently.

dprantl

How did I miss this thread until now... would it be possible to add the ability to change the engine temperature vs. fan speed ramp with this new controller? Earlier cars can just put in a lower temp fan switch, but newer cars cannot do this.

Dan
'91 928GT S/C 475hp/460lb.ft

Lorenfb

"Depends... modern FETs are much more resistant to heat and normal wear/tear. To that end we may use similar, but much more modern FETs."

Hardly the issue! The problem is NOT with MOSFETs in the original design, it's the design
itself that's the problem.

"I'll get these values into the model and we'll nail down a final circuit schematic."

A replacement unit without an analysis of the original unit and whether there's
a simple solution????

Read here for more info: https://rennlist.com/forums/928-foru...ive-fixed.html

dr bob

Dan--

You can dink with the controller response easily by adding a resistor in parallel with the sensor input to the fan controller. Pretty easy mod, done at the controller connector under the cover by the passenger seat. This isn't something I publish, because owners would end up with fans running all the time, masking other cooling system deficiencies until the fan motors give up. Owners look for a low and rock-steady gauge reading, which requires a great radiator and a low-hysteresis thermostat, along with fans running way too much.

dprantl

Sure, you can fool it with a resistor in series, but it would be pretty nice to have something built-in as long as it wouldn't raise the price/complexity much.

Dan
'91 928GT S/C 475hp/460lb.ft

danglerb

That is kind of the trick, improve on stock reliability and cost while adding a feature.

fraggle

I'm going to add some sort of sensor bypass to my "box" so I can kick the fans on full bore when I know I'm going to be stuck in traffic for awhile - before I end up with heat soak of any kind. It happens a lot here in VA with crummy traffic and high, humid temps at the peak of summer.

That said, I'm also going to put in a TC somewhere with a digital readout so the gauges don't fool me.

dr bob

If your AC is running, the fans are already at full speed.

The factory system is amazingly responsive to cooling requirements without a lot of owner 'fiddling'. That's why I choose not to share details on how to make the fans run earlier/cooler. Think about it-- There is really no real need or desire to add engine cooling at any time that the thermostat is less than full-open. The full-stroke range on the thermostat is somewhere in the 10º to maybe 15º range in my experience, so full-open happens somewhere around 200ºF with the factory thermostat. The gauge will run higher in the summer than in the winter, maybe 15º difference. It's very normal, definitely OK, engine certainly doesn't mind. It's why the temp-II sensor is allowed to detect water-bridge temps over 190º, hard to believe but true! It's a pee-sycho-logical issue with owner's and how they see the gauges. Get used to it, get over it, and invest your worries on something that's actually important.

[/old and crabby mode]