Override Cooling Fan

Override Cooling Fan

Postby ozguy7 on Sat Dec 02, 2017 8:17 am

Hi all,
I've recently installed an electric cooling fan using the provided connector and relay in a 2012 MN.

I'm looking to wire up a switch to turn the fan on manually. I've tried looking up to the trigger on the relay but this doesn't work. Id also like a an led to illuminate whenever the fan is running.

Appreciate any help as a little stuck on the easiest way to go about it.
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Re: Override Cooling Fan

Postby dieselweasel on Sat Dec 02, 2017 10:58 am

I'm not the man to talk about wiring but all of my switches have leds on them, i have blue, red and orange when the switches are on. This is how I bought them.

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Re: Override Cooling Fan

Postby RHKTriton on Sat Dec 02, 2017 11:27 am

O'guy; assuming you're talking AC fan, you'd have to find the trigger wire from the ecu to the ac fan relay. This probably gets pulled to ground by the ecu to activate (you'd have to confirm wiring diagram and/or meter). You could install a switch that performs the same task in parallel, that also grounds the negative end of a LED indicator. You would have to have some knowledge of electrics pursuing this method or you could damage the ecu.

Alternatively, I'd suggest sussing out the polarities that appear on the actual fan wires and simply install another relay and switch to drive the fan. This provides an independant backup to drive the fan and keeps you away from any ecu wiring.

On my electric radiator fan, I put in an override switch as both backup to the thermostat and as a means of blowing some air through the engine bay after a hard slog.
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Re: Override Cooling Fan

Postby dieselweasel on Sat Dec 02, 2017 1:35 pm

I like your alternative suggestion rhk and the backup switch idea, i would do that for that exact reason.

Ozguy, if you can be bothered, could you take a couple photos as you go for the forum? I think it would help anyone who is in the the same situation, me for one!
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Re: Override Cooling Fan

Postby ozguy7 on Sat Dec 02, 2017 5:06 pm

Think I'm going to go the route of installing another relay. I tried looking into the existing relay which worked well for the led indicator but experimenting with a switch to the relay trigger has just resulted in a blow fuse.

Happy to post some pics just got to get some suitable current wire for the new relay as I've only got small stuff.
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Re: Override Cooling Fan

Postby RHKTriton on Sat Dec 02, 2017 11:33 pm

Just a bit of 2.5 to 4mm2 stuff from battery - relay - fan should be fine. For wiring back into the cab I suggest a bit of seven core trailer flex.

This gives you some spare circuits for 'future' projects and you only have to run it once.

Just keep checking polarities as you go and no more fuses should end up on death row.
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Re: Override Cooling Fan

Postby ozguy7 on Sun Dec 03, 2017 8:33 am

Probably a dumbass question but I'm wiring up the relay. I've got the relay output to the positive wire on the fan. I've got the trigger to the switch. Battery positive to relay input.

Where should the ground go? Just battery negative to relay ground? Do I need to hook the relay ground to the fan ground as well?
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Re: Override Cooling Fan

Postby ag9111 on Sun Dec 03, 2017 8:50 am

Fan 0v goes to the vehicle body.
Where you are picking up the other side of the switch determines where the other side of the relay goes to.
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Re: Override Cooling Fan

Postby ozguy7 on Sun Dec 03, 2017 9:07 am

Thanks. I'm splicing into the fan wires after the existing relay. I want to retain the existing functionality.

The new relay input is connected to battery. Trigger is connected to switch. Switch ground is connected to battery negative. Output of new relay spliced into fan positive.

Just not sure if I need to spliced into fan negative and if so where it needs to go to.

Cheers
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Re: Override Cooling Fan

Postby ag9111 on Sun Dec 03, 2017 10:44 am

I think you have that wrong.
I suggest you google some wiring diagrams
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Re: Override Cooling Fan

Postby ozguy7 on Sun Dec 03, 2017 12:06 pm

Got it working

Relay input to battery positive. Relay negative to battery negative. Trigger connected to switch.

Relay output is spliced into Fan positive after existing relay in fuse block. Operates normally and can also be turned on manually via switch.

Just gotta sort out an led for when the fan runs :)
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