stewi2

The electric cooling fan on my 2001 A6 2.8 goes on full blast every time the A/C is on (it sounds like a siren). It turns off when I switch the A/C off or in econ mode.

I've seen several threads that talk about this happening when one of the two electric fans is blocked or broken, causing the fan controller to compensate by pushing the remaining fan to the max. Now my problem is that my A6 with the 2.8L V6 only has one fan (verified via the Bentley manual). It's located behind the radiator on the passenger side (labeled V7 in the diagrams). But the other fan (the one that is in front of the radiator on the 2.7T - V177) isn't there.

Three questions:

1. Did I get a lemon and they forgot to install the second fan ? Did Audi make a design mistake and leave out the second fan ? My in-laws, who we bought the car from and who bought it new said it's always been noisy like that. Even their mechanic told them that the noise is normal on this model. I think that's complete bunk.

2. Is the second fan installed somewhere other than in front of the radiator ?

3. Or could my fan controller be fried ?

stewi2

Thanks for the quick reply, Alan :-)

makes total sense for it to go to 2nd speed on hot days when the engine's heating up (I'd rather have the noise than an overheated engine). But mine actually does that as soon as the A/C comes on, even in the mornings when the engine is cold. Wondering how the two speed mechanism works. Is it the controller sending two different voltages to the fan ? Or is there some mechanism on the fan itself that does that when send some signal from the control module ?

-- Stefan

Zaphodb17

I'm having problems with my 2001 A6 2.8L, too. However, my fan is not coming on at all. No low speed or high speed. I've been wondering if the fan controller is bad, or if the brushset in fan motor is at the end of its life. I've disconnected the plug by the power steering resevoir and applied power to the fan feed and then it runs, but not at the high speed I've heard it run when it used to work properly.

I also believe all the 2.8s came with one belt/viscous coupling driven fan and one electric fan. My fan does NOT come on on any speed when the A/C is turned on, leading me to believe the fan motor is bad or the controller is bad. I guess the next step is to check for power from the controller (I've already replaced the temp sensor/switch in the rad and that made no difference. Has anyone ever had a fan controller go bad? How does one test that? Any info would be appreciated. Thanks

stewi2

Have you seen this article ? It's about the 2.7L with the dual electric fans, but some of it does seem transferrable: https://www.audiworld.com/tech/eng65.shtml

-- Stefan

Zaphodb17

Thanks, Stefan-the cooling control module in my 2.8 Quattro may indeed be fried, but there definitely is only one auxiliary (electric) cooling fan on the 2.8 ATQ engined A6s. My car has 140k on it and when I applied full current to the fan power/ground feeds, nothing happened until I smacked the fan with a heavy object. Then, it started to run rather slowly. If I kept whacking it, it seemed to pick up speed. So first thing for me was to R & R the fan and motor and see what transpired. When I checked across the power leads with an ohmmeter, I got infinite resistance until I whacked the unit and rotated the fan. Then, if I jiggle the fan blades just right, I got a reading. so, in my book, the fan (probably just the brushes) is history and I've now got one on order. Once I get that and install it, I'll move on down the diagnostic tree. I'm hoping that the control module isn't burned out, but like the above poster indicated, most times manufacturers set things up so that the expensive parts blow before the 50 cent fuses do...

stewi2

Lol - you whacked it with a heavy object - that's funny :-) As for the control module I would think you could test the fan voltage with a multimeter and jump the pins on the thermal switch plug as described in the article. Once you got you new fan, I'd be curious if it actually does runs at different speeds.

stewi2

Thanks Alan,

to me it doesn't sound like a bad bearing, but very much like the sound it would make the engine's about to overheat (except mine's not even close to overheating).

Guess I'll test the controller next. I've also considered the idea of simply retrofitting a second fan, since the control module seems to be the same between engines.

Zaphodb17

stewi2-just a quick update, there are indeed two speeds to the secondary fan. When I start the car, the aux. fan doesn't run. When I turn on the A/C, the aux. fan comes on at a first speed. If I'm stuck in traffic and it's hot out, every once in a while you'll hear the aux. fan kick up to at least 3 times its normal speed. On my car, the old fan had been bad for a long enough period of time that I think it started to cook the connectors on the fan control module. The fan did not run when I first plugged it in and I had to unplug the heavy (like maybe 10 gauge) connector to the module and use a pick to tighten up the contact area of each female terminal. Now everything seems to work fine.

stewi2

Thanks for the explanation. Now I know what's normal :-) Just need to figure out why mine seems to skip the low speed and go straight into overdrive.

stewi2

So I was all proud of myself for identifying the thermal switch as the culprit (jump one set of wires and the fan runs in speed 1, jump the other set and it runs in speed 2). So I replaced it, and it made zero difference. In fact, the old one wasn't even broken.

This made me look at the wiring diagram and realize that the reason my fan runs on speed 2 when the A/C compressor is on has nothing to do with the engine temperature, and all to do with the AC pressure:

* The fan runs in low speed if either the A/C head switch is on (even in Econ mode), or the engine temp triggers the first level in the thermal switch

* The fan runs in high speed if the engine temp rises to the second level in the thermal switch, OR THE HIGH PRESSURE SWITCH ON THE A/C COMPRESSOR TRIGGERS.

As far as I can tell, the A/C pressure is somewhat dependent on the ambient temperature, and it appears to take a bit to build up. So the fan doesn't actually become noisy until the A/C compressor has been running for a while.

I have no clue how frequently the A/C high pressure switch (F129 in diagrams) is supposed to engage and whether this is indicative of some issue with my A/C, or whether this is all just because of the humid North Carolina summer ;-)

Here are a couple diagnostic links:

http://www.vaglinks.com/Docs/Audi/C5...calTesting.pdf
http://mk1tt.montebellopark.com/radi...107453823.html