michael0156

The fan control relay (#2) is good (swapped it out with the horn relay). If I short the switched connections on the relay the fan runs, so power and the wires that carry it are good. For some reason the relay won't turn on.

I don't know the location of the high pressure switch and the Temp sensor. According to my Haynes manual they both have a red/green and blue/red wire attached to them and both the switch and sensor can independently energize the fan control relay.

On the engine I have located two sensors connected to the cooling hoses. One is a two connection switch (red/green and blue/red wires). I don't know if this is the cooling fan switch or the overpressure switch. The other sensor is a four wire thermo-switch which turns on the over heating light and operates the temp guage.

I cannot locate a third temp/pressure switch.

The Haynes manual shows the red/green wire of both the fan control switch and the high pressure switch going to pin 15 on the fuse panel and contact 85 on the relay.

I tried a continuity check from the switch to the top of the fuse panel, but I do not get a short. I read about 7K ohms. A voltage check, with the ignition key on, gives me a reading of about 5 vdc on both wires. When I look at the bottom of the fuse panel there is no red/green wire going to relay #2.

Help!!! Is there anywhere to get a good wiring diagram and a schematic for my Audi?

What could be the possible causes for the relay not switching on?

Thanks,
Mike

RussB

Its near the bottom, on the rear face. It contains two switches -- one closes at about 95 deg C (which allows current to flow to the fan speed 2 relay); the other closes at about 102 deg C (which allows current to flow to fan speed 3 relay). It has three contacts.

If your wiring is okay, it sounds like this thermoswitch may have failed.

I've found the Bentley schematics to be adequate. The generic one in the Haynes manual is essentially the same.

michael0156

I've replaced the thermoswitch. Thanks for the help in locating it.

Before I replaced the thermoswitch the cooling fan would not come on at all. After replacing it I have a different problem. The fan still won't come on when the engine is running, but when I turn the ignition off and the radiator is hot, the cooling fan comes on at low speed. When I turn the ignition on, without starting it, the fan turns off and stays off after I start it.

I removed the connector from the thermoswitch and shorted the connector's 1st and 3rd terminals and the 1st and 2nd terminals with the ignition off. The fan did not switch on. I turned the ignition on (without starting) and I had low speed from the 1st and 2nd terminals when I shorted them and a higher speed when I shorted the 1st and 3rd terminals of the connector that goes to the thermoswitch. Neither of these speeds were as fast as what I get when I short the load carrying contacts of the fan relay in the fuse panel.

I checked the new thermoswitch (bought from Auto Zone) by placing it in boiling water and ensured that I had a short between 1 and 2 , but I did not check that the high temp terminals were shorted when heated higher. I also did not check the orientation of the thermoswitch short relative to what connector terminal shorts made the fan run.

The only thing I can think of at this point is that the switch was manufactured backwards, or the plastic piece with the keyway was put on 180 degrees out when it was attached to the thermoswitch brass.

HELP! Anyone have any ideas?

Mike
michael0156@earthlink.net

ArlingtonVA

I have the same problem with my 87 5000s
The fan runs fine when the ac is on but doesn't run at all when the car running without the ac. Also, the fan only seems to run when i turn the car off. what finally resolved this problem? thanks millst005@comcast.net