Cooling fan not cutting in.

[Rower]

I have tried over riding the otter switch and can hear a contact at the fan , sounds like the clunk when you turn on the ignition and the starter moter is stuck, the fan overide switch operates the fan ok.Any ideas folk. I assume I will need to remove the rad to get to the fan assembley ?

[rzrz]

Had the same problem. When overriding the otter switch I heard a click from under the dash, which made me think the relais of the fan was fine.
In the end the relais appeared to be faulty.
In your case the problem is likely to be caused by a defect in the relais or in the wiring from relais to fan.

[Rower]

Thanks rzrz, what does the relay look like and were is it likeley to be located ?

[Paul V]

Relays in the S are in the passenger side foot well at the top of the fuse box. Try swapping the highlight one over to see if the fan then works.

[Rower]

Cheers Paul I will give it a try tonight, i assume the relay is a replacable unit ?

[Paul V]

Yeah, my local motor spares shop had one in stock.

[Rower]

Checked relays in fuse area all seem to be OK,definate click coming from fan area, is there another relay there.The fan itself works fine using the overide switch. Any advice gratefully received.

[s27]

Rower said:

Checked relays in fuse area all seem to be OK,definate click coming from fan area, is there another relay there.The fan itself works fine using the overide switch. Any advice gratefully received.

Any bad connections on the wiring from the Otter switch, Cannot remember how it was wired up, but there was a connector block situated towards the bottom of the rad, near chassis, cannot recal if the overide went through this, may be worth checking and cleaning the connections at this point, I had to do it once at that point.

Steve Parker

[Rower]

Cheers Steve, I will be down there tonight !

[GreenV8S]

Rower, I haven't been paying much attention to this thread but originally you said the fan didn't work when you shorted the otter switch but DID work when you used the override switch. Its common to wire in a 'fan on' LED when the override is added, but I assume when you say it works with the override, you mean the fan goes round rather than just the LED coming on? In which case, it should also work when you short the two wires together at the otter switch. But maybe I've misunderstood you?

[Rower]

No, you have it correct Peter, the overide switch def puts the fan on ,but no cut in from the otter switch,just a sort of clunk from the fan side if the rad when i short it out.

[GreenV8S]

A conventional fan override has exactly the same effect as shorting the otter switch out. Yours seems to be behaving very differently though. As far as I can see the possibilities are either your override is wired up in a very unusual way, or the thing you are shorting out is not the otter switch, or you are not successfully shorting it out. Where is it, what does it look like and exactly what are you doing to short it out?

[HarryW]

Rower said:

I have tried over riding the otter switch and can hear a contact at the fan , sounds like the clunk when you turn on the ignition and the starter moter is stuck, the fan overide switch operates the fan ok.Any ideas folk. I assume I will need to remove the rad to get to the fan assembley ?

I really don't understand the problem , so the overide switch opertes the fan , what isn't clear to me, having a thicky moment here so bare with me . Are you saying the otter swich doesn't work or the fan doesn't .

Just re-read the rest of the posts so you are saying you can hear a relay/noise when the fans should come on via the otter switch coming up to temperature but the fan still does not run as you would expect .
OK then just checked the bible its quiet astraight forward circuit. The otter switch uses a seperate fuse from the fan supply which might explain the relays being heard buit the fan does not run. The otter switch uses a shared 15A fuse along with relays and the fan uyses a dedicated 25A fuse, according to the bible they shoud be both on the bottom row .

1. Check these fuses by pulling them out and double checking they really are in tact, measure them with a meter if poss.
2. Next does the overide switch cabling run to the same fused supply that normally powers the fan , this can be proved by removing the 'normal' engine fan 25A fuse and try the override switch again, does it run , if it does then it doesn't use the 'normal' supply, therefore was the 25A fuse OK .
2. Next if all fuses are OK then perhaps the supply from the 25A fuse is not getting to the fan via the relay,is the rlay really OK
3. Next assuming you understand the circuit diagram I think you will have to cold check the circuit wiring paying particular attention to the override wiring and make sure that it hasn't bypassed the 'real' fan supply wire , this can be discounted if it is a recent fault and that it has worked in the recent past .

Let us know how you get on, failing that if this is outside your electrical knowledge then it should take a vehicle electrician no more than 15 minutes to find out whats wrong .
I hope this helps...............
Harry

[Rower]

GreenV8S said:

A conventional fan override has exactly the same effect as shorting the otter switch out. Yours seems to be behaving very differently though. As far as I can see the possibilities are either your override is wired up in a very unusual way, or the thing you are shorting out is not the otter switch, or you are not successfully shorting it out. Where is it, what does it look like and exactly what are you doing to short it out?

It is the unit strapped to the rad hose, I remove the spade end terminals and then connect the wires together using another piece of wire.

[GreenV8S]

Hmmm, that all sounds fine, the plot thickens! This suggests that either this otter switch i snot the one wired up to the fans, or the override is not wired up conventionally.

If you have a moment, I suggest you try two tests. First, with the override in the 'off' position and the ignition on, disconnect each of these wires in turn and see whether it has a voltage on it. One should have 12V and the other should be earthed. This shows the otter switch is wired up to something, presumably the fan relay. Second, when you turn the override 'on' do either of these voltages change? (Normally, I would expect to see the 12V pulled down to earth. But based on what you've found already I'm pretty sure you'll get a different answer.)

[Rower]

Thanks Peter, Steve and Harry, I will get on and try and sort it................or take it to an auto electrician, I will let you know.