Cooling fans

[marcus]

It's only just started happening on my S3 and that is, the cooling fans come on immediately the ignition is turned on. Cold or hot engine.

I've searched for previous posts and guess that it's either the thermostatic otter switch or the relay (of which it only has one underneath the radiator shroud), which is at fault. There are no separate manual switches that have been inadvertently left on in the car.

I don't suppose anyone knows how I can test either? Thanks.

Marcus

[Mountain King]

Oh how I wish my S3 was like that last year, my fan didn't turn on at all one very hot day in London.....

Firstly use a multimeter with a conductivity test function to check if the relay has not got stuck in the closed position, you will have to pull the plugs from the tabs to ensure there is no short. Likewise check the otter switch for a similar problem, or simply pull the connector from the switch,this will break the circuit, does the fan then turn off?


W1 and W2 on the right go to the low power coil that takes the signal/power from the otter switch.
C1-C2-C3 are the high power switched part for the fans and this is where the problem may be. C2-C3 is closed in the cold position, C2-C1 is closed in the hot or activated position.

your problem is that it is permanently closed, and not closing on request, so the following is not really pertinent, but :
To check, and the otter switch is not the best tbh, particularly if it is still the original, I actually may have a spare replacement lying around, give me a day or two to check. But to test yours, just take it out of the housing which is likely very corroded (i may have a spare of that also along with the gasket which you must replace). Connect a battery and light bulb up to create a circuit, or use a multimeter with a conductivity tester and suspend in to a pot of water along with a thermometer and start to heat slowly it should switch around 75-80 degrees C, mine is 78oC, just make sure the connections do not short.

Simon posted the following helpful wiring link
http://dl.dropbox.com/u/8496016/S3%20Fan_Relays.pps

and the full wiring diagram in the knowledge base:
https://dl.dropboxusercontent.com/u/849 ... wiring.pdf

my guess would be the relay, they can get very hot next to the radiator and over time corrode and short out or get stuck in one position.

Andy

[marcus]

Andy,

Thanks for your detailed action plan.

I appreciate it's basic wiggly amps checking a switch such as the otter switch, which I have now done.

The circuit is permanently closed, confirmed with a continuity meter.

The fans also turn off if one pulls a connector off the switch.

All checked in situ as I presume to take the switch out you have to drain the coolant.

Yes please if you have a spare switch and gasket.

Marcus

[PeterE]

I got fed up with the quality of Otter switch replacements, mine like Andy's got stuck in the open position but a PO had fitted a manual override switch in the dash position occupied by the HRW switch in a fixed head.

Permanent solution was to fit one of these: http://www.coolcatcorp.com/Merchant5/me ... e=Cooling3 and no problems since, the supplied BMW-type switch opens at a lower temperature too and although the fan cuts in more frequently it keeps a bit cooler.

[marcus]

Right, thanks Peter.

I'll have a litte think.

Wouldn't really want it to fail in the open position.

Marcus

[Mountain King]

Totally agree Peter,
I have a new system, not the cool cat but similar.

i can have a rummage around in the garage in a day or so, but Marcus, personally I'd fit a modern equivalent, trust me, if the radiator boils and you need to replace the gaskets and skim the heads etc, it is expensive!!!

50 quid for a modern version is money well spent.

[marcus]

OK that's decided then Andy/Peter thanks. An upgrade.

I'll get onto it tomo.

Marcus