Gretch

other than the various sensors triggering cooling fan operation, does the fan control module vary the speed of fan operation? IE are there more than "on" and "off" modes?

jayc67

WSM page for 87 and up says :

"The output stage recieves a square signal from the control unit. The output stage contains 2 mutually independant output-stage modules with separate protective circuits: each module controls a separate cooler fan.

If a fault occurs, the cooling-air flaps are opened to 100% and the intact fan operates at full speed, while the faulty fan is switched off. A check is made every 20 seconds to ascertain whether the fault persists"

The fan voltage is variable depending on the water temp and the freon , and it's simple on or off dependant on the transmission temps for auto cars.
There are 3 speed settings.....

Picture of the 3 function charts:

ErnestSw

IIRC there are three fan speeds available through the controller. There is no continuous variability.

T_MaX

I would have to look it up again. But up until the GTS (year?) the final stage (under the hood) oscillated the fan voltage which would give one the impression of more than three fan speeds.

MikeN

I guess it depends on how you define "continuous variability". I guess you could say the fans are continuously variable using three different speeds.

I would tend to believe that there are really only three speeds.......although the fans take a few seconds to ramp up or down between those speeds, hence the illusion of continuously variable speeds across a given RPM range.

Gretch

Jayc67,

Thanks, and facinating......

What effect does the intake manifold temp sensor have? is the output variable for that sensor too?

ErnestSw

I think the intake manifold sensor acts like an on/off switch for the cooling fans and my impression is that it's in parallel with the circuit, ie. it only tells the fans to run (at low speed) after the engine stops if the temperature is above a given level. As it's wired from the factory I don't think it could be usefully modified for increased cooling while the engine is running.

Gretch

I am not interested in making modifications to this system, (right now) I just want to know how it works. I notice that after I turn my car off, if the fans are running, they step through two speed levels before they stop. That experience doesn't square with your comments above.....what am I missing?

ErnestSw

My best answer is I don't know. Our cooling systems are different in that you have (or had) slats and you don't have the recirculation system. It's possible that my system goes through two speeds after I turn the car off, but if it does I haven't noticed it.
Are you hunting down a problem?

jayc67

My 87 S4 also goes through 2 speeds when shutting down if I really het it things up, and that matches with the coolant temp function chart above. I also have an A/T so that might contribute since there is a function for trans fluid temp as well. Looks like there is a step down from approx 10V to 8V as the coolant temp drops.

The manual I have does not mention any of the more advanced functions Ernest has. My books are current through the '90 model year so I can't comment on changes made after that.

Gretch

I still have the slats........currently no plan to remove them..........BTW they are a real bitch to get to anyway, fortunately they are not in my way. the AWIC radiator fits quite nicely between the flaps and the grill, with no interference to flap operation.

I have changed out the stock the fans on my car because of the imposition of the blower and air box immediately behind the radiator. The kit uses 4 smaller fans mounted in pairs on either side of the airbox. Additional air flow can be induced with a large single pusher fan in the front. Choosing how to wire the fans requires I understand how to diagnose the fan control functions. I just wanna know what I should be looking for, (and up till now have been to lazy to RTFM...........need a "********" Icon here)

The drivers side fan seems to have always come on first on my car, but that is not consistent with the info jayc67 posted about the fans working in unison, with failover mode defaulting to 12 volts for the working fan. However, when I close the intake plenum sensor, both fan circuits operate. Jayc67 says his fans step through two speeds before shut down (with the key off, ie plenum sensor driven operation). I am in learn mode........That is all that is going on...

BTW, anybody here ever try waterwetter of the NAPA brand "enginekool"?

Gretch

That is interesting....so the plenum sensor does not cause the fans to run at full capacity.....ie they don't get 12 volts................oooooookaaaaaaay....

Old & New

I believe there was a change to the latest controllers that allowed the fans to run at full battery voltage, as opposed to capping it at 12V.

Gretch

Cool, (pun intended) where are the controllers located, is an upgrade straight forward?

Garth S

"BTW, anybody here ever try waterwetter of the NAPA brand "enginekool"?"
No, - Does it improve the taste of straight anti-freeze?