Okay, brain is working even less than usual. Need to draw it out perhaps to get my thoughts straight on this deal, but thought I'd check with the electric gurus here to see if they had a good solution.

Have a new electric radiator fan about to install. The temp switch will be located in the radiator in the threaded fitting. It is a factory radiator fan switch for a mid 80's Camaro. Should complete the circuit when temp is reached.

The issue that is throwing me a bit is this. The fan is two speed. There are three wires. The instructions say to ground one wire and then use just one of the other power wires (does not matter which) with a 20 amp fuse on it if you only want to run the low speed. If you want to run the high speed then connect the other power wire through a 20 amp fuse to run at the same time. Hope that makes sense.

What I want to do is in general operation I only want it to run on high to be the primary cooling for the radiator. THEN, when I shut the car off, I want to have the fan run on low speed for a while to cool the system down.

My question is how to wire the relays for this. With the standard 4 prong type relays my initial thought was to have two relays running the two power wires for the high speed. The instructions say you can run them together, but if for some reason the single 30 amp fuse (in this instance) blows then the fan obviously will not operatate at all until the fuse is replaced. If the fans power wires are run on individual systems with the 20 amp fuses, then if you develop a short on one at least the fan will still run on low speed as the other power wire will still be feeding it.

I'm thinking that I might need a third relay to run the ignition off circuit and somehow run another temp sensing unit for it like one of those probe type that stick through the fins. Only thinking the different sensing unit as I've heard that the run on with the ignition off can be rather excessive when using the tank type sensor. May not be an issue, but only want the fan to run a few minutes on low to cool the radiator and also perhap circulate some of the heated engine air out of the engine compartment.

Anyway, probably a confusing rambling post as usual. Hope you can make head or tail of it.

Thoughts?

Cheers

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From Mopars to classic Minis and back to Mopars in 19 years flat!

Will work for roast chicken crisps!!

2 relays and 2 diodes........


Power side of relay

Fuse-----> Relay ------> Fan (a,b)

Coil side of relays:

Relay 1:

Fuse----->Diode----->relay------>temp switch
(same fuse as power supply for that relay)

Relay 2:

Ignition source ----->Diode------>relay--------> temp sensor....


Diodes are not needed if seperate temp sensors are used (you could have them staged for low/high operation of fan) otherwise you need the diodes to avoid weird power flow situations (make a wiring diagram for yourself)

Relay 1 will always run as long as the temp switch is on.
Relay 2 will only run if the temp switch is on AND the ignition is on.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Thanks for the reply. Okay, almost got it with that.

So the diodes are there to stop a reverse flow of the circuit making the other side of the fan operate? Have I got that right? A diode is basically a gate that allows flow only one direction.

Not really done much with diodes, but I assume they maybe come in different values etc? What would the suggestion be for that? Radio Crack supply for diodes okay do you think?

Cheers

_________________
From Mopars to classic Minis and back to Mopars in 19 years flat!

Will work for roast chicken crisps!!

Yep, only one direction. Without the diode current could make it back to the ignition side of your electrical system (thru the coils in the relays) and do strange things. Or trigger the relay after the fuse blows on the other side.

Radio Shack 1 amp diodes will be fine. 2 for $.99 or 25 for $2.79. I'd get the 25 and you're set for future projects.

http://www.radioshack.com/product/index ... age=search

(print the radio shack page off and bring it with you, finding stuff is easier that way...........)

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

THANKS!

_________________
From Mopars to classic Minis and back to Mopars in 19 years flat!

Will work for roast chicken crisps!!