i thought the fans always were in a "hot" mode and would turn on even if the car was sitting while off?
the temp switch would dictate when they turn on and off...regardless of the ignition...right or wrong?
your manual should show which leads are "hot at all times" to the fuse box that you can tap into, or, if you prefer to use the ignition switch, then you can tap into an unused fuse space on the front of the fuse box.
it depends on what people want you can run a fan by just turning on the ignition, by flipping a swich, or with a thermostat. I want to Keep It So Simple, because my electronic work fine right now, I do not want to touch the fuse box(also hard to work on since under driver side feet). So I just want to wire the fan to an already run wire, either a 20 v fuse, or if it is a 30 can I just put in a little 20 on my positive. Also which wire is hot on ignition that I can tie into?
you'll need a wiring diagram for your year vette. if you want, trace the hot wire from the battery to the engine compartment. from there you should be able to see what wires are hot at all times.
dual fans are not a "plug and play" thing. you need to tie them into relays,as well as the temperature switch on your block. some fans sense heat from the radiator. i'm not sure what your set up is. and be sure that a 20 amp fuse is what they require.
is your car stock? or minor or major engine mods? why are you going to a dual fan set up? or do you have heating problems with it?
I always run relays not switches for handle any descent power. You can get a relay for about $5 for 30 amps at most parts stores. Hook the relay to any power supply then use the key to energize the circuit. If you take an volt meter and start checking wire with the key on, find a live wire convenient located, turn the key off and see if it turns off. If so you found a keyed live wire. You are only using it for energizing and not for power so the drain is very small.
If you use a keyed wire to run the fan it might blow the fuse immediatley or in the future since the ignition is not meant for that power load.
Use the relay and take power anywhere , even off the starter if you want but use a relay.
If you have a switch to energize the relay you might overlook it and cook the motor or if someone else is borrowing the car they might not know about the switch. It is safer to use a thermo on off switch to energize the relay or leave it on everytime the motor is turned on. This might not be good in the winter.
true, but he still has to run it thru the temp switch to signal when it needs to turn on. the reason i mentioned using an "always live" circuit was because the temp switch would turn it off when the sensor realized it was cool....even after he shut the car down and walked away. they would only run for a minute or so. most cars do that any ways.
again, he needs to know how the dual fan set up he has is configured. does it have a radiator mounted sensor? does it have wiring to plug into the temp switch? is it configured for a/c? i'm not crazy about anything manual for the fans.
i do agree with you on the use of relays. the fan motors draw some heavy current.
I checked the link to SPAL and did not see a how to wire type document. I would think the "proper" wiring would be a latching circuit that allows the fans to continue running if you turn the ignition off after driving from point A to point B. That's how most of the new cars I've seen are wired.
Once the engine is cool and the thermostat disengages the fans the circuit is no longer powered.
One could argue based on the mass of the motor, heads, etc that once the temperature is below the thermostat setting that it will not rise above that again due to ambient temperatures. Following this line of reasoning you could use just an always hot circuit and count on the fans disengaging when the temperature falls below the thermostat set point. Depending on the failure modes of the thermostat this may or may not have a significant likelyhood of leaving the fans running an indefinite period of time and draining the battery. The latching circuit would be susceptible to the same failure mode unless an additional circuit with a timeout was added. This would all become far too complicated adding a bunch unneeded electronics.
Either wire it hot or wire it switched and be done with it.
Running the fan after engine shutdown probably derives from the now widespread use of Aluminum for the engine block and heads providing more rapid heat dissipation ergo the fans continue to circulate air through the radiator and around the compartment and out through whatever designed escape path. This is probably also directed at "baking" of components under the hood.
I have no measurements available, however it seems that the underhood temperature would rise rapidly say after an hour on the highway you pull off and shut the engine down. The thermostat temperature on a small block V8 should be 200 F, when everything suddenly stops the coolant/block temperature probably rises 50 degrees or more. The ambient underhood temperature probably rises above 100 F.
There may even be some surface temperature safety aspects to this design. I'm going on a little bit of supposition, however the domestic and import auto industry is implementing their electric fan cooling systems to continue to run after shutdown so there is obviously a reason. Whether or not it's a good reason may be up for debate.
When I install electric fans on street rods I build ,I run a wire direectly from the hot terminal on the battery & always use a relay. I also let the fan run after the engine is shut dn to reduce heat soak to the carb.......DR Don
on my 69, I pulled unswitched power from the starter motor. I ran it through a relay that is keyed. It also is tied to a thermostat switch on the water pump. It comes on and off as the heat rises but turns off with the key.
On my brothers quarter mile firebird I did the same but gave him an over ride switch on the console so he could leave the fan on without the key if he should so decide.