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Discussion Starter #1
It has two prongs.

Is it just one prong to the fan negative lead and the other to a ground?

I'm not using a relay because I'm not putting a manual switch in the circuit anywhere.

How can I test the functioning of the circuit and switch with the engine disassembled? Can I wire it up and heat the probe with a torch to see if the fan comes on?
 

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It has two prongs. Is it just one prong to the fan negative lead and the other to a ground?
Yea, it looks like you have an Alfaholics p/n COO131, which from their website seems to just be a simple SPST, normally-open switch.

I'm not using a relay because I'm not putting a manual switch in the circuit anywhere.
Sorry, that didn't make sense. Relays save the coolant temp switch from premature failure due to carrying high current. Whether or not you have a manual switch has nothing to do with using a relay.

How can I test the functioning of the circuit and switch with the engine disassembled? Can I wire it up and heat the probe with a torch to see if the fan comes on?
A torch would have too high a temperature and might damage the switch. I'd use a coffee cup filled with boiling water and connect my voltmeter probes to the switch terminals. Set the meter to measure resistance - it should go to zero when the switch closes.
 

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A SPST switch simply interrupts a current path. Maybe it is just semantics but one side is not ground and the other 'hot' (when the switch closes it'd be shorting to ground). It would typically go in the path of one or the other (usually the hot side).

A simple way to test is with a pot of boiling water.
 

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Discussion Starter #6
A SPST switch simply interrupts a current path. Maybe it is just semantics but one side is not ground and the other 'hot' (when the switch closes it'd be shorting to ground). It would typically go in the path of one or the other (usually the hot side).

A simple way to test is with a pot of boiling water.
That’s what I meant — the same color wire coming out both sides of the switch.

I will do the test you suggest.
 

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The switch will work equally well in either the hot or the ground side of the relay coil (or fan motor if you ignore the good advice about relays).
 

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Discussion Starter #8
The switch will work equally well in either the hot or the ground side of the relay coil (or fan motor if you ignore the good advice about relays).
I am taking the relay advice. It has a brown wire that is supposed to go to ignition. Where is that? It is different from the red wire that is supposed to go to the starter motor solenoid.
 

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You can just wire it up to unswitched power. Fan'll be able to run with the ignition off but that's a good thing. Easiest way to do it:

Run +12V from the alternator or the starter to terminals 86 & 30 of the relay. Put an inline fuse on this wire close to wherever you're drawing power from.
Run a wire from 87 on the relay to the positive terminal on the fan, then another wire from the negative terminal on the fan to ground
Run a wire from 85 on the relay to one terminal of the switch, then another wire from the other terminal on the switch to ground
 

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Discussion Starter #11 (Edited)
You can just wire it up to unswitched power. Fan'll be able to run with the ignition off but that's a good thing. Easiest way to do it:

Run +12V from the alternator or the starter to terminals 86 & 30 of the relay. Put an inline fuse on this wire close to wherever you're drawing power from.
Run a wire from 87 on the relay to the positive terminal on the fan, then another wire from the negative terminal on the fan to ground
Run a wire from 85 on the relay to one terminal of the switch, then another wire from the other terminal on the switch to ground
Like this?

So helpful! Thanks!!

Two of the relay terminals go to the same place — a power source. That’s the part I didn’t get.

A million thanks.
 

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You can just wire it up to unswitched power. Fan'll be able to run with the ignition off but that's a good thing.
Gubi is right that this is the easiest way to do it, and yea, when the fan continues running with the engine off, it won't kill your battery.

But it isn't elegant. After all, your belt-driven fan stops when the ignition is off, so why should your electric fan keep running? I always run one more wire, connecting the relay like:



Switched power can come off the coil "+" terminal; the relay draws very little current so the coil won't miss it. The thermal switch in the radiator can either interrupt the power to terminal 86 or the ground from terminal 85.
 

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But Mad North-Northwest
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After all, your belt-driven fan stops when the ignition is off, so why should your electric fan keep running?
Coolant continues to circulate under convection after shut down, and there's still quite a bit of heat in the hot parts of the engine that gets transferred to the coolant. So I'll often see the fan cycle once or twice after turning the engine off, which is nice to help get a bit of extra heat out of things.

So I like having it wired up to unswitched power, but in the grand scheme of things it probably doesn't make much of a difference.

Also you've got your 30 and 87 flipped on that diagram: 30 is 12V in, 87 is output. It'll work fine the way you have it but it's not correct from a terminal numbering designation and the next owner will probably curse you.
 

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Also you've got your 30 and 87 flipped on that diagram: 30 is 12V in, 87 is output. It'll work fine the way you have it but it's not correct from a terminal numbering designation and the next owner will probably curse you.
I didn't draw that diagram; just found it with a quick Google search. So you're saying that everything on the internet isn't 100% accurate? I'm shocked!

Coolant continues to circulate under convection after shut down, and there's still quite a bit of heat in the hot parts of the engine that gets transferred to the coolant. So I'll often see the fan cycle once or twice after turning the engine off, which is nice to help get a bit of extra heat out of things.
I see your point. I'm just saying that Alfa engines were designed to withstand slow cooling after shut-down, with no fan running. From an efficiency point of view, it may be desirable to let the engine stay warm if your stop will be brief.

I know that many production cars are wired to allow the fan to continue running after the ignition has been turned off. But I get antsy walking away from a car with a high amperage device still running, even though I know that the radiator temp. switch should shut it off well before the battery dies. Even the delayed headlight shut-off on 21st Century cars makes me nervous - and yea, it's probably irrational.
 

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Relay question

Since i am ignorant to electronics can you guys be specific as to the relay as to model numbmber or or specs so i can pick one up at pep boys or autozone or one of those stores thanks john
 

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this diagram looks easy to follow (to me at least!) except I am not sure you need the diode thing (?)

a normal 4 pin SPST relay, with pins 30/85/86/87 should do it, one with its own provision for a fuse is neater than in-line fuse (like you'd use for a starter relay)

https://www.alfabb.com/bb/forums/7650689-post10.html
 

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this diagram looks easy to follow (to me at least!) except I am not sure you need the diode thing
You're right about the diode. Suppressor diodes across the relay coil are common in circuits where the relay is switched by a transistor. But for an application where a mechanical switch is controlling the relay coil (e.g. an automotive fan), arc suppression isn't an issue.

Putting a suppression diode across the power terminals (#30 - 87 in that schematic) would make more sense, as the fan motor generates a LOT more inductive kick-back than the relay coil.

a normal 4 pin SPST relay, with pins 30/85/86/87 should do it, one with its own provision for a fuse is neater than in-line fuse (like you'd use for a starter relay)
I agree that in-line fuses are pretty "mickey mouse", especially in a mission-critical circuit like a fan. However, if you locate the fuse in the relay, then the wire between the power source (say the alternator or battery) to the relay is unfused. And that wire is just as likely to get damaged as the wiring between the relay and the fan motor. Best to locate the fuse as close to the power source as possible, even if that means an in-line.
 
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