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marvo

Electric coolant fan overide switch

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Hi all, I am installing an simple single electric fan in my 72 240Z V8 SBC 305 and want to include an overide switch in the car to allow me to switch on the fan manually if the thermo switch ever fails to kick the fan in. I am thinking this would normally be wired to operate the relay coil to allow voltage to the fan however I am thinking if I wire in a 'heavy duty' switch into the fan feed supply across the relay then this would work if the relay ever failed also. Any thoughts? Many thanks Marvo.

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What about a manual fan in case the electric fan fails?! Kidding aside, you can only take the redundancy so far. There are many many cars on the road with thermostat switches. I would just get a high quality switch and leave it at that. If you are really worried about it, you could order a big heavy-duty toggle switch and wire it from the feed to the output on the relay and use it as a manual bypass, mcmaster has 30amp toggles. Again though, now you have another point of failure, what if the toggle fails closed and you can turn the fan off? It just never ends.

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Thanks for the prompt reply and yes I am a bit of a worrier!! I will take a look at switches available over here to see what suits me best, I do like the idea of the 'overide switch' actually overiding both relay and thermo switch, failing that I will open the hood and blow cold air over the engine!!! Mind you here in England it doesn't get too hot anyway!

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I think the normal way ie a switch in the relay control circuit seems to be the favourite then just carry a spare relay in the glove box just in case of relay failure!

 

Thanks guys I will get on and wire the car up now!

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Fan relay dying isn't really something to be super worried about. Standard Automotive relays have a mechanical endurance of about 1x10^6 cycles and a electrical endurance of about 1x10^5 cycles.

 

If you want to be a little more safe you could setup the relay "always on" so your switch pulls it off. Then if the switch or its supply dies, the fan will kick on.

 

In an emergency situation you can always hot wire the fan on and drive home. 

 

But seriously. Wire it up nicely (good solder, heat shrink) and dont worry. 

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