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[Debs.]

Arriving home today engine at 'normal' temp, I could hear the single (rear of rad.) fan coming on-and off in quick succession; `sounded like a loose wire/plug......upon checking, the fan sensor-plug and fan-plug seemed tight and correctly inserted.

I checked the wiring and discovered the part of loom has been trapped twixt the battery and the radiator side support metalwork: although the loom branch at that point has heavy gauge (I`m assuming fan) cables in it, the only one that had 'failed' (rubbed-through/verdigris-corroded) was a single-one of the thinner ones, which I simply soldered back together and insulated with heatshrink.

Ran the engine back upto temp., and the two front fans now work (something I haven`t heard them do for years)...the temp stabilised at 85/90 C. (ish) with the two front fans (quietly) cutting in and out as a radiator-fan would normally do...but, no rear fan (which normally makes a heck of a din) and which has been the only fan I`ve heard working since I`ve owned the car.

So!......has lack of front fans up `till now (which I guess I`ve corrected by my soldering) meant the rear fan has had to do all the cooling when the front ones should`ve worked?

Before I investigate further into the loom near where the pinching/abrasion damage was; for, there might be damage to conductors leaving insulation intact, I need to know which is the normal sequence for cooling: which fan/s (i.e front or rear) start/cycle first and which is the auxilliary; cutting-in (only) when engine temp rises above the normal fan-cyclic range.

*BTW: I know the front fans are also aircon. fans.

[Kevin Wood]

I'll have a look at the relay logic later but on my car the front fans run at half speed all the time the aircon is running.

I believe, if you leave the aircon off, the front fans (and possibly the rear one too, although not sure) come on at half speed for the first stage of cooling and then all 3 fans come on flat out at higher coolant temperature.

The fans themselves are switched by a collection of relays in the box next to the battery, and it takes a bit of head scratching to figure out what's going on.

There are several inputs including a couple of stages of coolant temperature, a couple of stages of air con temperature and, I believe, pressure and also an input from the aircon compressor clutch signal.

There is a small square test connector in the relay box which can be used to scope out the function of the system. I believe the correct signals to see here under various conditions are covered by a howto, although I might be wrong.

Kevin

[Andy B]

.......
I believe the correct signals to see here under various conditions are covered by a howto, although I might be wrong.

Kevin

It's on the ABS forum ...... 'donated' by someone in the States 

[Debs.]

Thanks Kevin.....the aircon needs a re-charge, so the low pressure run-switch takes the aircon fans/compressor logic off line (and out of the equation).....so, the front fans are working 'just' to rid the engine/radiator of heat.

The front fans surely are working at half speed...`lovely quiet sound.
I think I haven`t seen/heard them working at all for over three years.....so the resoldered wire must`ve brought them back to life.
The single/rear fan has only ever worked 'flat-out'.....on or off (very loud) and alone; I`m guessing it has been shouldering the cooling burden alone because of the fault in the front fan`s circuit.

I have the Haynes laughter book.....so, will have a look at the 1999 circuits and see if I can fathom the fan-logic from the wiring diagram`s relays/resisitors/cabling....and also, will have a paw through the forum 'how-to`s.

[Kevin Wood]

I have the Haynes laughter book.....so, will have a look at the 1999 circuits and see if I can fathom the fan-logic from the wiring diagram`s relays/resisitors/cabling....and also, will have a paw through the forum 'how-to`s.

I suggest you pour yourself something strong beforehand.

I have a vague recollection that, whereas the front fans are run with the motors in series for half speed and in parallel for full speed, there is a resistor below the battery that is used to run the rear fan at low speed but something is telling me that was not on all models. Either that or the resistor has burnt out.

I'm guessing that what you lost was the signal from the first stage of the fan switch, as this starts the front fans at low speed.

The second stage of this switch starts the rear fan at max. speed and switches the front fans in parallel, but since the first stage is required to power the front fans they were never working at either speed.

Well, you can rest assured that your Omega will survive this heatwave now.

Kevin

[Debs.]

.......
I believe the correct signals to see here under various conditions are covered by a howto, although I might be wrong.

Kevin

It's on the ABS forum ...... 'donated' by someone in the States 

P.M sent......

[Andy B]

.......
I believe the correct signals to see here under various conditions are covered by a howto, although I might be wrong.

Kevin

It's on the ABS forum ...... 'donated' by someone in the States 

P.M sent......

Just seen ..... and replied     

[Debs.]

With the kind help of information sent by AndyB; I now see why the main rad. fan was surging as if there was a loose wire/plug (even though all seemed tight and correct): the brown and white wire that had been damaged by the battery crushing the fan/sensor loom against the sheet metal edge, was 'grounding out' to the sharp metal edge and 'effectively' switching the main (rear) fan into fast mode. (and then not).

The wire that was damaged/broken (and I re-soldered) was the one serving the low speed setting for all the fans....which now correctly work on low.

Andy`s info. makes sense of both thermo-switch`s various states and associated loom colour-coding.
I`ll give the system a thorough multi-meter test tomorrow to make sure non of the other cables in the bundle are suffering damage/corrosion/continuity problems.

Thanks again Andy!

[Andy B]

.....
Thanks again Andy!

       You're welcome!