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Hiding under a Rock
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Discussion Starter · #1 ·
Hi guys,

For whatever reason, the ECU/PCM is not giving the signal to the fan (via relay and fuse) but the fan goes when the A/C is on (as it should).

So What I'm planning to do is to install a separate fan controller which will trigger the fan.

To minimise messing about the existing wiring, I want to borrow the existing relay/fuse wiring and just tap the fan controller wire to existing trigger wire. Obviously I'll need to get the fuse/relay box out, flip it upside down to find and splice into the wire.

Any pointers?
 

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Little Megger
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You sure it's not just the resistor in the fan tray lower lhs that has corroded? That's the usual suspect. You'd get fan on full speed with a/c on, but not 2-stage fan speed.... ????
 
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Hiding under a Rock
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Discussion Starter · #3 · (Edited by Moderator)
You sure it's not just the resistor in the fan tray lower lhs that has corroded? That's the usual suspect. You'd get fan on full speed with a/c on, but not 2-stage fan speed....
The resistor looks ok but not sure how it works - looking at it, it has a resistor and a coil-looking thing wired in parallel. Is it a variable resistance resistor? If so, what are the resistance range?

The thing is the fan doesn't come on even with the temperature rising over 105 degrees - this alone wouldn't concern me but the rising level of coolant in the expansion tank makes me think that the fan should be kicking in sooner.

So if the ECU is not turning on the low speed fan (via the resistor) then it should turn on the high speed fan when it detects higher than normal coolant temperature, but it doesn't. So I reckon the ECU has lost the plot in that regards (there is another thread in the engine section - I've checked the wiring to and from fan and relay etc)

I suppose I can try bypassing the resistor by sticking in a jumper wire but I'm not holding my breath.

I've been driving on diagnostic mode and turning on and off A/C as necessary - not particularly safe and I want something simpler and reliable (hopefully).
 

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Little Megger
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That coil thing IS the resistor. Can you test it for continuity with a meter...also pull the connectors off and check for corrosion on them.. Once they start to heat up they can corrode quite badly.
Not sure what that other thing is... and I've thrown my old one out.
 
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Hiding under a Rock
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Discussion Starter · #5 ·
That coil thing IS the resistor. Can you test it for continuity with a meter...also pull the connectors off and check for corrosion on them.. Once they start to heat up they can corrode quite badly.
Not sure what that other thing is... and I've thrown my old one out.
I've checked the connectors and they are clean.

It must be variable resistor of some sort, may be the resistance goes up with air cooling the coil, then the fan speed will slow as there won't be as much demand for fan drawn air for cooling. I don't know.

I'll disconnect and jumper them and see if it makes the difference.
 

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Hiding under a Rock
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Discussion Starter · #6 · (Edited by Moderator)
I pulled the resistor and replaced with a 30A blade fuse (which happened to fit in the connector).

Will go for a run tomorrow and see what happens.

If the fan runs and/or the fuse blows (the fan fuse is 40A) then at least I'll know the wiring is good and bypassing it will fix it.
 

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Hiding under a Rock
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Discussion Starter · #7 ·
The ECU still didn't trigger the fan at 100 degrees so I manually turned it on by switching on A/C, the fan came on briefly and off. Needless to say the 30A fuse in place of the resistor popped. I hurriedly jacked the car up and put the resistor back on to cool the engine down.

This means the ECU is not triggering the fan low speed or high speed.

I assume at 100 degrees is low enough temperature for the ECU to stick with the low fan speed. I wonder when the high speed kicks in. It doesn't really make a lot of sense because by the time high speed fan kicks in, it would be well on its way to overheating.

I'm going to install the fan controller tomorrow, I just missed the delivery today.

I'll have to stock up on grocery and stuff just in case I'm in it for the long haul...

I assume at 100 degrees is low enough temperature for the ECU to turn on low fan speed. I wonder when the high speed kicks in. It doesn't really make a lot of sense because by the time high speed fan kicks in, it would be well on its way to overheating.
 

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Little Megger
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Hi, the fan speed is governed by the pressure in the a/c.....so if the a/c pressure rises it kicks the fan into full speed mode. Was told this by the guy who serviced and filled my a/c after I replaced the condenser.
I really don't know if the fan speed is also dependant on the coolant temp. (on my diesel Mondy the fan hardly ever comes on with UK temps) The facelift Mondy has got an electronic module in place of that resistor unit and is controlled differently, I think.
 
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Hiding under a Rock
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Discussion Starter · #9 ·
What I've read is, A/C clutch solenoid activates the fan.

It is beyond me why the temperature is not the main input for fan activation and the crusty old darkage resistor at the bottom of the radiator controls the fan speed.
 

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Hiding under a Rock
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Actually, I'll shut up now and hit the books first before talking.

Next to the cooling wiring diagram on the Haynes, there is A/C wiring diagram - although there is no reference to the cooling fan (well, not directly, as far as I can see) BUT there is one wire between two diagrams that has the same colour and both go to the ECU. I don't know if they are the same wire but I'll check it out later.

I'm not too concerned with that at this moment though.
 

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Discussion Starter · #12 ·
I managed to get the box off (well, off enough to access the wires - you can't really remove it completely unless thousands of connectors are removed from the housing)

I'll do a write-up with some photos when I finish the job, for future reference.
 

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Here is how to, if anyone is interested.

1. Remove battery and air filter box (this may not be necessary but makes things easier and it comes out in a jiffy anyway)

2. The fusebox is in two pieces, front half and rear half. And they sit in a entire fusebox housing. If you want to access the wiring on the underside of the fusebox, you have to get front and/or back halves off the fusebox housing.

If you want to remove the whole thing, it comes out in one piece, like so.

A. Remove a 8mm bolt between the fusebox and the airbox. (a big black arrow)

3TwbGUw.jpg


B. These two tabs are holding it at the forward end.

8nsHYcy.jpg


Slide the fusebox rearwards and tip it forward, then it comes out.

3. To get to the wiring underside, first remove the forward half. It's not necessary to remove the whole fusebox, but makes the job easier.

A. Undo the two connectors, blue and green. They were pretty tough to release.

B. Remove the 10mm nut in the middle.

C. Release the two tabs, circled in red (refer to the first photo).

D. Release the two tabs, circled in red per below.

Q36QHA7.jpg


The tab circled in black releases the lower shell of the front half of the fusebox but you need to get the front half out before getting to these tabs, as some are obscured by the rear half of the fusebox.

Here is the lower shell off.

mxvT59h.jpg


Here is the front half pulled out so wiring can be accessed.

HtIR2Fi.jpg


qFMi5ea.jpg


You can now access the rear half. It is similarly held in place with tabs right around. Unlike the front one, it doesn't have a lower shell.
 

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Little Megger
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that is really useful info! I bought a new fusebox shell years ago as the original had been part melted by acid, but I've never been able to work out how to dismantle the old one! Pity you can't somehow copy this write-up into the Fordwiki... but maybe make it a sticky..?
 
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