Hey gang, 89 S4 with fan issues. As usual, one would not work which caused the other to run twice as fast. Now, neither one works when I turn on the AC. (shouldn’t they come on immediately after I turn on the AC?).

The fans themselves have been replaced with new parts in the past year. The fan controller has been replaced with a rebuilt unit. The fuses are not blown. WHAT DO I CHECK NEXT?

Are there relays that run the fans or controller? I’m at a loss.

 

Most likely the fan amplifier at the front edge of the engine bay.

92861842100

 

Test also the control module, passenger side under the radio amplifier cover (92861841800).

 

is there a relay or fuse that runs this control module?

 

Take the connection off of the finned unit at the front edge of the headlight bar and clean it
Replace both fan fuses make sure they are tight fitting if not add some solder to the blade use deoxit 100

 

Jumper the connection on top of the intake and turn on the key. The fans should come on. If they don't, check the sensor on the bottom front of the radiator by jumpering those wires. The next thing to test would be the fan signal amplifier already mentioned above.

 

Run a fused connection from your jump post to each FAN, work backwards from there looking for 12 volts, if the fans do work with direct 12v applied

Dave K

 

Fuse # 28 and #29 for the two radiator fans
Relay XVIII related to the cooling flaps and it is the only relay witch i know related to this module (94461511900).

 

Replace your Ignition-X relay. I think it is in position IV in your '89. You can try swapping in your horn relay to see if this restores your radiator fan operation.

 

Thanks guys. I’ll give those suggestions a try.

 

OK,

I replaced both fuses and the relay. One of the fans now work as it should. I added deoxite to the finned unit up front (its a refurbished one from 928sRus, less than a year old). The fans are less than a year old.

I checked for 12V at the fan that isn't working. I got nothing. To check it, I turned on the key and the AC. One fan came on and I tested the wires that plug into the fan. Is that the way to test it? I'm not sure how to jumper the fans from the temp switch on top of the intake.

 

The temp switch on the intake should have 12v one one pin, when the intake gets hot enough it will close and the the fans will run.
So all you need to do is pull the wires off the temp switch and short them together (fans should run) if you have 12v on one of the pins.

 

Swap the wires to the fans and see what happens - if the other fan now works and the previously working fan doesn't then the fans are both OK and the issue is upstream - in the fan controller, wiring, fuse etc. If the fan behavior stays the same (the same fan fails to work) then its a fan issue.

The relay has nothing to do with this (flaps only) so ignore that - but since something you did restore some function I'd be suspecting the fuses. You can test the fuses electrically and that is what you should do. On the face of the fuses (where the amperage rating is) there are 2 small dimples allowing you to probe the fuse blades while in circuit. Using a DVM ground one probe and test the voltage at the top of fuse #28 & #29 (for an '89). These are the inputs to the fuses (on '85 and later cars) you should have battery voltage there. Then test the bottom (output) of the fuse - you should also have battery voltage there. Try this again with the car running and the fans supposedly active - measure the bottom of the fuse - do both still have battery voltage. If yes to all then the fuses are OK and the fan amplifier looks more likely as a cause.

Alan

 

Ash,

As I recall the switch closes at higher temperature so to simulate operation one has to short the two cables.

Check to ensure you see voltage on the feed cable to the PWM unit- if there is no voltage going in for sure non will be coming out.

The control unit next to the passenger seat sends a control signal to the PWM unit and both fans should run at the same speed. When the inlet manifold switch is made both fans should run at about 2//3rds of max speed. If the controller senses that both fans are not running it ramps up the operational fan to full speed.

The ac switch is used when testing because it turns on both fans at 2/3rds of max speed irrespective of engine temperature. When the ac is switched off the fans will not run until the requisite temperature in the water bride is reached and that is about 80C as i recall. The PWM unit is a solid state high frequency switching unit that turns power on/off rapidly - this simulates modulating the voltage and the fans operate as though they were being modulated by voltages in the range of 9V to 12 volts.

 

I shorted both wires together and both fans ran. This is looking more like the finned controller unit. A rebuilt unit should last longer than 6 months correct? The fuses are new and i'll check those like the above recommends.

​​​​​​​Ash