To save money and effort im going to use a dashboard mounted swtich to activate the fan.

My plan is to have it so you cant turn on the fan unless the ignition is on, but the fan will continue running after the ignition is switched off.

I have drawn this schematic...can someone have a look at it and just make sure that i havnt made a silly booboo...

In an ideal world the fan would stay on for say five mins after the ignition was turned off and then switch itself off....but I dont feel like going into the design of a timer circuit...

[Edited on 27/3/07 by tegwin]
Rescued attachment Fan latching switch.JPG

You don't appear to have a thermal switch involved, or have I missed something? You could simplify even more by just wiring a thermal switch to a permanent feed - the fan will always switch off when the temperature drops below 90 degrees or so.

[Edited on 27-3-07 by RazMan]

I dont have a thermal switch, because the cheapest thermal switch and mounting that would go in the water hose was £30...Would be nice to have one, but for that money is it worth it...

But surely your circuit will just switch the fan off when the ignition is switched off.
I can't see why you have a diode in there really.

My logic is that once the fan switch is switched on it passes a +ve ignition feed into the relay coil. As soon as the relay closes the fan comes on and the supply to the fanswitch/relay gets switched to +ve perminant supply....If you turn off the ignition the fan switch is still powered so the fan will remain running...


If you turn off the fan switch with the ignition off the rlay will open and there will no longer be a supply to the switch so the fan cant be reactivated until the ignition is back on....

The diode is there to prevent the +ve perminant supply feeding back into the ignition circuit when the ignition is off causing engine overrun....

Complicated, but I think it should work?

Pah, just wire a normal fan thermo switch in then that to a relay for the fan and then make it permanently live. No need at all for a manual over ride at all.

Ahhh I see it now! My brain is a bit slow this morning (due to strong pain killers).
Ingenious and quite simple really .... especially if you cant fit a thermal switch.
I think you can get latching relays which do a similar job.

[Edited on 27-3-07 by RazMan]

I always prefer a manual switch for the an and no rad switch, when its on its on!!

Tis ok...there is something about ciruits like that that confuse me aswell!

Just out of interest, what aftermarket thermo switches are most people using and where do they get them from?

In my case I used a Polo rad with a built in switch (it might be worth looking in the scrappy if you don't fancy a new one) but I think Vauxhall ones are commonly used.

TBH I have never seen the point of a manual overide switch - that's what the thermal switch is there for

[Edited on 27-3-07 by RazMan]

I have a really weird rad...not sure what its from...but it actually fits in the car...It doesnt have a rad temp swich on it....

If I do have a thermo switch its going to have to be an inline pipe jobby....

Where is the cheapest place to get one?

Used a Golf (v' similar to Polo) rad and Golf switch on mine.

Having seen Merlin seize his engine on the way to SVA as he was in traffic and forgot to look at the temp' gauge I really would advise you fit a thermo' switch!

If you can't fit a switch into the rad then weld a threaded boss to a piece of pipe and fit a cheap thermo switch in there (fiver from motor factors).


HTH,
James

quote:

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Complicated, but I think it should work?

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The cheap solution, find a busted Polo Radiator, take the fan switch out then hacksaw into the rad header and you will find a brass nut that the switch threads into. Go to plumbers merchant get a 28mm equal tee saw the T leg down and solder the nut to the stub, its easier if you file the corners of half the nut so it locates in the tube!

Here is one I did earlier, the hose fits nicely onto the plumbing bit and the solder ring holds the jubilee clip nicely!


Caber
Rescued attachment Photo_022407_001.jpg

Yup. I'd certainly go to the effort of having a thermo switch. Whether you bother with a manual overide or not is up to you.....

We have a Micra Rad fitted with it's own thermo-switch - wreckers £15.

We also mounted a dashboard override for trackdays...

Steve

This won't work unfortunately, there are two fatal flaws:

1) The fan will run as soon as you switch the igntion on via the diode.
2) There's no way to stop the fan once it's running!

Adding a second diode in the wire running from the fan to the switch would solve the first issue, but not the second. To switch it off you would have to break the circuit somewere (with e.g. a normaly closed relay) in order to break the latched action of your relay.

The cost of a thermo switch is trival in comparision to the consequences if you forget to switch a manual one on...

[Edited on 27/3/07 by MikeRJ]

with mike on this one!



infact a normal diode wont work because the fan is quite some amps..

anyway before the fan fit the thermoswitch

and feed the thermoswitch true a Fuse direct to barrery +

then if igntion is off and engine temp is higer as fan switch for example a (92 / 97)
(ITS HIGHER THEN 97degrees!!) then it will switch on the fan..it will switch off when 92degrees is reached..

the manual button will need to be connected to the motor terminal (just as the terminal switch) and to a ignition feed)

and that case its never a problem to switch on the fan below 97degrees (if its off) and you cant forget to let it stay on when ign is off

Sow from Ign live to switch from switch to motor terminal (behind the th switch)

from fuse box to fuse from duse to TH switch from th switch to motor..

Easy really and no diode involved..

Tks

i got my adjustabe thermo switch free with my fan. all the PACET - Clovafan Club Range come with them on rally design.
but you need to buy a fan though.