Fans don't work with engine running

[cavebloke]

Hi Guys,

Anyone had this fault before: fans work fine when the ignition is on (they both come on with the thermostat) but when the engine is running they don't work at all. They cut out as soon as I engage the starter motor and don't come back on. I'm guessing a faulty earth is the culprit but has anyone got any other ideas?

Cheers,

Simon

[andy43]

That's weird. I'd test at the fans (there's connector blocks close to them that can get weathered and fail) for power, at the otter switch and also try shorting the otter switch out, and then try and find the pink/green wire in the loom that sends a signal to the relay(s). From memory the pink/green wire is earthed to switch the relays. Checking relays are actually clicking is another good one. The nearest earth would be below the rad - could be that? Not had to mess with the fans myself (yet..) other than fitting a manual override on the steering column, hooked up to that pink/green wire in the passenger footwell. Oh, and is it standard, or does it have a modwise fan control kit, 'cos that would mean different checks.
You'd think with the engine running they'd be more likely to work, not pack up altogether...

[Steve_D]

Have you been doing anything with the alternator?
reason I ask is the earth wire from the otter switch grounds on a fixing on the body of the alternator. If you have the wires off it is easy to mistakenly connect it to one of the unused field coil connections. This is possibly earth until you start up then it is +12 so the fans don't work.

Steve

[cavebloke]

andy43 said:

Is it standard, or does it have a modwise fan control kit, 'cos that would mean different checks.

It's standard in terms of wiring but has an aluminium radiator.

Steve_D said:

Have you been doing anything with the alternator?

No, I haven't touched the alternator. But I suppose it could be an internal fault possibly. Thanks for the idea Steve.

andy43 said:

I'd test at the fans (there's connector blocks close to them that can get weathered and fail) for power, at the otter switch and also try shorting the otter switch out, and then try and find the pink/green wire in the loom that sends a signal to the relay(s).

I think: I know that all the wiring for the fans is functional as they behave correctly when the ignition is on but the engine not running (ie they don't run when the car is cold and run when the car is hot). My feeling is the fault might be something in the ignition circuit (or alternator as Steve suggests) that is making an earth go live or something. I don't think it is starter related because the fans don't come back on once the starter disengages.

I guess some more testing is required to work out the problem. It doesn't seem like a simple common problem.

Cheers,

Simon

[andy43]

I reckon Steve's right. New otter switch earth could sort it, but isolate the old one in case it goes live with the engine running.

[cavebloke]

Steve_D said:

Have you been doing anything with the alternator?
reason I ask is the earth wire from the otter switch grounds on a fixing on the body of the alternator. If you have the wires off it is easy to mistakenly connect it to one of the unused field coil connections. This is possibly earth until you start up then it is +12 so the fans don't work.

Steve

Just to close this topic with the solution: you were quite correct Steve. Whilst I hadn't been fiddling with the alternator it turns out the earth connection had worked it's way loose and was only functioning very poorly. So thanks for pointing me in the right direction.
Cheers,
Simon