cooling fans

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Dollywobbler
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Re: cooling fans

Post by Dollywobbler »

Must look into this on mine. It's hopeless having the fans on a switch when there's no temperature gauge! The fans are very quiet on mine, so perhaps they're only working on the slow setting. They certainly shift enough air.
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mat_fenwick
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Re: cooling fans

Post by mat_fenwick »

There could potentially be a relay (or the associated wiring) at fault in this case. The offside fan receives current from the earth side of the nearside fan via the NC contacts of a changeover relay when the fan switch 'hot' contacts are closed, and hence runs at half battery voltage. When the 'very hot' contacts are closed (i.e. the thin green wire on the fan switch is earthed), this energises a second relay to supply the offside fan with full battery voltage, and also switches the changeover relay to the NO contacts and routes the current from the nearside fan to earth. As this works correctly when simulating 'very hot', the changeover relay is working correctly but the second relay does not appear to be.

EDIT - just realised/remembered something (as Jaba already mentioned) - for the offside fan to work correctly at full speed the 'hot' contacts of the fan switch also need to be closed as well as the 'very hot' contacts, to give the O/S motor a path to earth. I've added a bit to what Brian suggested:
Brian wrote:4. Connect the bottom of the U with a link wire to the left, should run the fans on slow
speed.
5. Connect the bottom of the U with a link wire to the right leaving the left link in place, Should run the fans at
high speed.
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Re: cooling fans

Post by RobC »

Many thanks Mat, that makes sense! Will test again.

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Re: cooling fans

Post by rutter123 »

on my t/d they both come on together on low speed, to my knowledge ive never had them running on high speed, i will run a check on mine and let you know.
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TizzyD
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Re: cooling fans

Post by TizzyD »

Thread bump! Sorry

I've been suffering a number of issues with my BX of late and the cooling fans are another issue on the mountain...
Brian wrote: 1. Pull the plug from the switch.
2. Look at the plug and configure as a U.
3. Ignition on.
4. Connect the bottom of the U with a link wire to the left, should run the fans on slow
speed.
5. Connect the bottom of the U with a link wire to the right, Should run the fans at
high speed.
Ive just done this test, pulled the plug off and linked the Left and Right (up rights) of the | _ | plug to the bottom connector of the U in the middle and had no response from either fan. I had the key set to the first turn on the ignition (accessory). I don't need to have the engine running do I ?

My understanding from other threads is this:
Left connected to bottom of the U = both fans at slow speed
Right connected to bottom of the U = N/S at full pelt
Both connected to bottom of the U = both fans running, faster than low speed but not as fast as the N/S fan on its own.

The fuse by the glove box looks ok, and I know there are relays by the washer bottle on the bulk head and I will try changing these for new relays to see if its these are at fault.

There is also a relay behind the N/S headlight in a blue case and a couple of thickish black wires, the connections look quite corroded but is this anything to do with the fans ?

Ultimately, I want the fans to work correctly on their own, but I also want to wire in manual override switches for low and high speed so I can control them at will for my own peace of mind.

So two questions:

If changing relays brings me know joy, where should I look next ?

And...

Anyone got a simple way to wire in a pair of manual switches to activate both fans at low and both at the higher speed ?
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Re: cooling fans

Post by Way2go »

Do you have aircon on the TZD? If so the fans should run when the aircon is switched on and Ignition is ON (not just accessory position). This way doesn't depend on linking anything for test and fans will run when engine cold and even if the aircon gas needs recharging.
I've switched a/c on when sitting in stationary traffic queue before now to bring fans on permanently to give extra cooling to the rad.
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Re: cooling fans

Post by TizzyD »

Nope, just a standard TZD with twin fans, no air-con.

Will try the test again tonight with the ignition fully on and see if that's why nothing happened.
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Re: cooling fans

Post by RobC »

Yeah the cooling fans only work with ignition on (ie 2nd click) - that's caught me out before too!
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Re: cooling fans

Post by TizzyD »

#-o #-o #-o

Right, fans work with the ignition on the second click!

What I found was:

1) Left connected to bottom of the U = both fans at slow speed = just as expected :)
2) Right connected to bottom of the U = N/S at full pelt = again as expected :)
3) Both connected to bottom of the U = O/S running really fast but only on its own, not both fans so this doesn't seem right with what I've read elsewhere :-k

So it seems that I have a potentially dead rad fan switch as when the car over heated bringing both orange and red temp lights as well as the stop light I don't remember hearing the fans running at any speed. Having just had them running there is no way you could miss the noise so some lubing maybe in order.

So if I want a manual over-ride switch for say, just both fans at low speed, could I just connect a switch between the +12v on the left hand side of the U and the earth at the bottom of the U ?

Excuse my bad drawing and hand writing...

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Jaba
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Re: cooling fans

Post by Jaba »

I think you have got it right. What seems not to be working correctly is when both connectors are earthed at the same time you do not have the LH fan working at high speed as well. Your results do not make too much sense (on paper) as you can get both fans working at high speed but not together.
Are you sure you are earthing both sides simultaneously and getting only the RH fan ?

The rad connections behind the front grille are prone to corrosion so they are worth checking.

You can test your rad switch in a heated pan of water with a thermometer and electric meter to verify or otherwise its functioning. Its probably just as easy to just put another switch in though. Very little water escapes if you take the switch out from a full but unpressurised system.

As an aside my TD almost never has its fans running and I reckon that the TD rad is a bit over specified for the job.

If you really want an overide switch the what you suggest is correct but its arguably better to have a manual override to put the fans on at high speed, i.e. a two pole switch earthing both sides simultaneously. The fitted switching system is more than adeaquate IMO and I have never felt the need with a temp gauge fitted to have a manual switch as it always just works as it should and the gauge will tell you when the fans should be running and you can certainly hear and feel them at high speed. So vigilance here will pay off. Bear in mind that head gaskets always eem to fail anyway.
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Re: cooling fans

Post by TizzyD »

Thanks for the reply Jaba.

I'm sure I'm only getting both fans running simultaneously at low speed when I bridge the left terminal to ground. No other combination bring both fans on together but I'll check this again tomorrow to confirm.

Could it be possible that a relay has failed thus meaning that when both left and right terminals are grounded for high speed, it's not throwing the connection to bring on the second fan (N/S) but the circuit allows for it (N/S fan) to operate on its own when the right terminal is grounded ?

As for the manual switch, what I might do is extend on your idea and have a three way rocker switch so that position A (up) is low speed, position B (middle) is off and position C (down) is high speed. This would give me free reign over which fan speed I choose to manually over-ride too.

Would changing the fan switch run the risk of introducing air into the cooling system which would then need to be bled again ?
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TizzyD
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Re: cooling fans

Post by TizzyD »

Right, had another poke around and after a few attempts both fans now run at high speed when both left and right terminals are grounded to the bottom of the U on the plug and they make a hell of a racket! I could hear a relay click for the first couple of tries and then they both came on at high speed.

Will look into fitting a new fan switch and I might go for one with a lower temperature setting to bring on low and high speeds sooner so it doesn't have chance to overheat.

Also, does anyone know what this is behind the N/S headlight ?

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Re: cooling fans

Post by Jaba »

Glad you have confirmed the high speed running.
That pic is of the glowplug preheat timer. It is usually protected by a sort of plastic bag.
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Re: cooling fans

Post by TizzyD »

Ah fair enough, I gave all the connections on it a clean as they had got quite corroded and now the car starts like a dream! But then the new Exide 760A/77Ah battery and fresh glow plugs would also help :wink: :lol:

Ordered the bits to wire in a manual switch for the fans and will have a go at rigging it all up so I can have manual low and high speed fans.

I still think the fan switch itself has failed but I'll change that at a later time as Ive spent enough on coolant in the last 8 weeks.

Where is the best place to feed wires into the cabin from the engine bay ?
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Re: cooling fans

Post by morningglory »

Tempted to bung a manual fan switch in for good measure. Good thread resurrection. I've just installed an aftermarket water temp gauge (not as offensively gauche as it sounds, for all you purists) and ran the sender wire through the big grommet behind the fuses under the glove compartment. It comes out near the battery.
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