pindonesia1999

Hello all,

New to the forums and a8. Used to have a URS4. Trying work through all of the kinks of a newly purchased 1997 Audi 3.7 FWD a8.

I have been scouring the forums to figure out an overheating issue in traffic.

Did a complete flush of the cooling system with new Audi coolant.

Aux fan does not come on when the AC is on AUTO.

It doesn't seem to be the thermostat, as the car cools easily while driving and stays cool - 3HR + highway drives.

Fuses in the passenger footwell good - 60 AMP and smaller fuse

Hooked up direct 12v to the cooling fan and it comes on.

I am assuming it is the relay - or the fan control module. Not able to find either. I unfortunately don't have the manual yet. Is it in the passenger footwell? I have accessed that - not sure which relay? Any advice would be greatly appreciated.

Thanks so much!
Dan

silverd2

The cooling fan control (resister board) gets input from a few sources...climate control head, thermal switch on radiator, AC high pressure switch, different relays for different fan speeds (relays on panel under driver's footboard...#3 & 4, center 2)...but if the fan is not working at all, my guess would be the resister board, just ahead of left front wheel behind fender liner, under left headlight:

pindonesia1999

Thanks so much silverD2! I will check the resistor board:

I found a write up on another site for older Audis, just wondering if the resistor is setup similarly to this:


"The 3 Terminals on the resistor pack are designated E1, E2, and E3.

On the 87-88 5000T/Q, E1 should have a Red/Brown stripe wire, E2 should have a Red/Blue stripe wire, E3 should have a Black/Red Stripe wire. The 89-91 200TQ shows E1 with a Red wire, E2 with a White wire, and E3 with a Black or Black/Red stripe wire."

Just wondering if E1, E2, E3 are similar, in that, the varying fan speed control: E1 low, E2: mid speed: E3: fast; on the Audi A8?

It's def. not coming on with AC, so I guess assume E1 and E2 are bad if it's not the relays. E3 should come on with temp above normal, that is not happening - so whole board could be bad. Would there be a way to bypass the resistor board and just get the fan spinning?

silverd2

Yes...same set-up.

Another test: Thermal switch on radiator has 2 switches built in...one that triggers low speed and one that triggers 2nd speed. Each of these send a signal through a different relay...so, if shorting both of these, one at a time, does not trigger the fan, it would seem to be the resister board at fault.
Wires brown to brown w/yellow stripe (terminals 3 & 2)should trip low fan speed.
Wires brown to brown w/blue stripe (terms 3 & 1) should trip 2nd fan speed.

pindonesia1999

Thanks so much SilverD2! I will give that a whirl and let you how it goes. Best, Dan

pindonesia1999

Hey Silverd2,

No luck jumping e1 to e3, or e2 to e3. Any way to bypass the board completely? There is one black wire coming off the fan connector on the female side that connects to e3 on the resistor board on top of one other wire.

Here is another good write-up that I have been following as well: http://www.sjmautotechnik.com/troubl...g/cooling.html

Thanks so much!!!

silverd2

Well, the black wire is just a direct positive to the fan. If you already ran 12V directly to the fan and it worked, you eliminated the fan itself as a fault. If you put 12v to that black wire, the fan should run at full speed..if not, it's just the wire.

The wire from the relay for high speed (3rd) actually is connected directly to that wire on the outside of the resister board and just runs 12V directly to the fan, without going through a resister. The board cuts down current for speeds 1 & 2.

If you shorted the thermal switch poles neither speed worked (plus the fan being OK), it sure sounds like the resister board is fried(?)

pindonesia1999

Its funny, I unplug the 3 prong temp switch. I take a tester to the female side yellow/brown wire and blue/brown, and get 12v with accessory on. Brown wire with accessory on, no 12v. I thought only the brown wire was to supply 12v to the temperature switch at first, and then, at certain temps, it would send 12v back on e2 close relay and start 2nd speed fan, and the highest temp, send 12v back to E3 to close the relay for the highest speed.

I'm starting to wonder if it is wiring somewhere. At a loss really.

Thanks,
Dan

silverd2

The brown wire is the ground only...the thermal switch completes the connection from each of the other wires (separately) when called for "thermostatically".
Shorting each of the other wires (one at a time) to the brown should run the fan. This imitates signals sent from the thermal switch. If no fan, then the resistor board (or wiring to it...less likely) is NOT sending the signal along to the fan.