# radiator fans



## thewolf (Jun 20, 2010)

Hi,

I'm opening this new thread trying to figure out how radiator fans work on the TT, since I have a small overheating problem with mine, see my other thread: viewtopic.php?t=219852

My 2001 TT (180HP) has two fans between the radiator and the engine: a smaller one on the left and a bigger one on the right and when the actual temperature (as per channel 49) reaches 98C the left fan goes on, while the bigger fan remains still. Same thing when turning on air conditioning (even with cool engine): only the smaller fan comes on.

Is the bigger fan also supposed to come on together the smaller fan? If so, something with my bigger fan may be faulty and that may explain the (small) overheating issue of my car.

I've searched around this forum and other places on the Internet for a reply to this question for the 1.8T VAG engine: some people state that the two fans should always be running together, initially at 1st speed, and then if the temperature gets really high, at 2nd speed, while others say that only the smaller fan should come on initially.

Can anyone check if their fans always run together (either turning on air conditioning or letting the engine get hot when car is not moving) or if initially just the smaller fan goes on?

I think even simply turning the air conditioning should start both fans and not just the small one, meaning that my bigger fan is faulty, but I'd like a definitive answer before I turn my car in for repair to the Audi shop.

Thanks.


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## Neb (Oct 25, 2007)

did you check the green fuses on top of your battery? The control the fans and could be blown


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## dpbayly (Mar 16, 2011)

Just popped out front started car up and switched AC on and yes both fans run...


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## peter-ss (Sep 3, 2008)

Looking at the wiring diagram the two fans are paralleled up so should be doing the same thing.


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## sierra (Mar 29, 2009)

I had the same problem and found the strip fuse to be blown and also the fan motor had burnt out. I bought a new fan and fitted it and all is working fine now.
Fitting takes a while as I removed the entire front end of the car


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## ryanmtt (Sep 13, 2010)

I have just had this issue and have just picked my car up from audi because the wiring to the fans were faulty, these parts were covered under warranty


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## thewolf (Jun 20, 2010)

So it looks like both fans should always be running together.
And since as soon as I turn the air conditining on, only my smaller fan comes on, I assume something is wrong with my bigger fan.

Where do I start checking what's wrong with it? Can it be tested with VAG-COM/VCDS?

Thanks.


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## TTwalshie (Jun 6, 2011)

Neb said:


> *did you check the green fuses on top of your battery? The control the fans and could be blown*


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## thewolf (Jun 20, 2010)

TTwalshie said:


> Neb said:
> 
> 
> > *did you check the green fuses on top of your battery? The control the fans and could be blown*


I checked the green fuses on the top of the battery and they look fine.
Also, if there was an issue with them, wouldn't the smaller fan also stop working?

Thanks.


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## peter-ss (Sep 3, 2008)

You may find that the resistor has burnt out on the larger fan and that it may still work on fast but not on slow.

It would be worth getting the engine hot enough (about 104oC) for the fans to run flat out and see what happens.

If it works on fast, but not slow, then the resistor has most likely failed.

If it doesn't work at all then the motor has most likely failed.

In any case it could be a wiring issue.


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## thewolf (Jun 20, 2010)

peter-ss said:


> It would be worth getting the engine hot enough (about 104oC) for the fans to run flat out and see what happens.


Is there an easier way to test it other than having the engine get that hot?



peter-ss said:


> In any case it could be a wiring issue.


How would I check for that?

Thanks.


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## peter-ss (Sep 3, 2008)

I wouldn't worry too much about the temperature reaching 104oC. My Mk1 used to do it all the time; I thought that it was normal as I didn't know that the fans were supposed to have two speeds.










The best way to check the wiring will be with a multimeter / test lamp to see of there's 12V getting to the fan or not, unless there's an output test for it on Vag-Com - Just mind your fingers.


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## thewolf (Jun 20, 2010)

peter-ss said:


> You may find that the resistor has burnt out on the larger fan and that it may still work on fast but not on slow.


What if I feed (external) power directly to the bigger fan? How can I force it to run at the slow speed and then to the faster speed to test the resistor?

Thanks.


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## thewolf (Jun 20, 2010)

sierra said:


> I had the same problem and found the strip fuse to be blown and also the fan motor had burnt out. I bought a new fan and fitted it and all is working fine now.
> Fitting takes a while as I removed the entire front end of the car


Were both of your fans out of service or just one, like me?

Is it really necessary to remove the entire front end of the car to replace a radiator fan?

Thanks.


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## John-H (Jul 13, 2005)

You can see in the diagram that the fans are wired in parallel and that on the slow speed each fan has a resistor. It doesn't matter what turns on the slow speed - Vag-Com, aircon, coolant temperature over 96 deg C (lower switching point) - they should come on together.

You can unplug the fan and apply 12V to it independently. You can even pierce the wire insulation with a pin and check 12V is applied to the fan as that's a little easier to get at. By this means you can also identify which of the three wires is which - one is 0V Gnd and the other two are +12V when activated.

I've not tried but I believe you can remove the fan without too much disassembly if you disconnect it from the plastic frame.


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## nunny71 (Feb 15, 2015)

hi 
just had the same thing but ac fan is making a racket and main fan is blowing slow . 
so just think this is a case of replacing both fans for piece of mind, even though I know its just the ac fan itself
after replacing coolant flange I noticed the car getting hot, so decided to look further and found the fuse ontop of the battery had melted along with the fuse in it,
so im going to run a bypass from the wire to the fuse and connect it directly to the terminal, with a separate fuse and wire, and replace both rad fans
hopefully job sorted

2001 Audi TT 225


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