Like I mentioned before you need to figure out the in-rush current. This is different from the sustained current, that will answer your question on if it's OK to power both at the same time.

**BUTT** I will say, to me, your best bet is an aftermarket controller that gives you the flexibility AND simplicity you're looking for.

I would relay and fuse each fan separately.  I don't know how much these draw at start up, you could measure it with a multimeter, but I'm going to guess they draw close to 30 amps at start up.  To avoid blowing a fuse you'd have to fuse a combined circuit at 60 amps, and then, if something went wrong with one fan and it shorted causing the fuse to blow the other fan now also wouldn't work even though there's nothing wrong with it.  So, for redundancy alone I'd fuse and relay them each separately. 

Whether or not the fans will operate at multiple speeds depends on a couple things.  A factory system would likely have more than two wires going to fans for such a system (which is what that Volvo fan control system describes).  Now, regardless of whether or not the fans use multiple windings for various speeds you could create a circuit that varied output voltage to in effect govern fan speed.  This could be done several different ways, but the real thing to consider is that by reducing the voltage you are going to be creating heat, because the way you reduce the voltage is by increasing resistance.  I'd be concerned about what that heat could potentially do to the wiring, etc.

IMO, this is all academic.  There's no practical reason to need two fans both operating at multiple speeds.  I still stand by a simple relay system, because there is basically nothing to go wrong, and its easily repaired on the road if needed.  Carry a spare relay and a spare fuse or two and the parts needed in your "just in case" tool kit still fit in the palm of your hand. 

I'm sure those fans were controlled by the computer in the OEM application.  If they are indeed multi speed I wouldn't suggest just hot wiring them to run just the high or low speed.  At that point you are going to need some kind of controller, or a more involved custom built system, but that would require knowing a bit more about the fans. 

This works really well, no power rush. Also some cars are coming out with brush less fan motors
https://ls1tech.com/forums/forced-induction/1906766-variable-speed-pwm-fan-control-under-25-less-diy.html

I'm going to run a Contour fan setup also, gotta do it on a budget for now until I can afford my Holley Sniper setup with the built-in fan control. Would this setup work using the factory built in resistor? See the attached wiring diagram. 

Last edited by 92vanguard (7/05/2019 8:22 PM)

92 vanguard, I thought this fan assembly is dual fan , not dual speed. I looked at pictures on the article, that is what I noticed.

Theres a resistor between the two plugs. Low speed to one side and high skips the resistor. Both fans run at the same time. Either high or low speed. AFAIK, the fans ground on a seperate plug. I used to own an SVT Contour and the fans run together, not individually.

That makes sense.  I'm a fan (heh) of its simplicity as well. 

The trigger point may require experimentation.  That's why I prefer an adjustable triggering mechanism.  I have mine set at 195, with a 180 degree t-stat in the engine.  This gives the coolant a chance to start circulating before the fan comes on.  This should allow proper circulation because it doesn't cool the coolant so much that it drops below the t-stat closing temp.  I found that even on days with the outside temp in the upper 90s and heat index well over 100 it still never got over 210, and mostly ran at 205 even on those days.  On cold days warm up still happens quickly and it runs closer to 180, which is still good for circulation. 

BUT, your setup may vary based on your radiator, t-stat, water pump, etc. 

One thing I'd advise is inserting a fail safe switch into the trigger wire for the high speed.  This way if something fails you can still trigger the fan by grounding the relay. 

92vanguard wrote:

Theres a resistor between the two plugs. Low speed to one side and high skips the resistor. Both fans run at the same time. Either high or low speed. AFAIK, the fans ground on a seperate plug. I used to own an SVT Contour and the fans run together, not individually.

First of all I lied, didn't through out the old electric fan. Found it while looking for other parts. Your right there is a resister behind that plug and the fans use a separate ground. I don't have the whole harness from the Contour fan but I have the fans, shroud and wires with it. There are some other control wires involved with the fan setup so I'm not 100% sure but I think your diagram would work. I would run a wire from your green wire to both fans positive leg, then a ground to both fans negative leg.

TKOPerformance wrote:

Start up amp draw of 60 is to be expected.
I would fuse each relay feed with a 40 amp fuse. 

So if it pulls 60 amps at startup, why would I use a 40 amp fuse?

Hmn, I suppose you'd need a 60-70 amp fuse then if it draws 60 amps on each setting (low and high).  I must be honest though, that seems really high.  My point was fuse it a bit higher than what it draws.  If its supposed to draw 60, but actually draws 61 you will constantly be blowing the fuse and having no fans running.  I would definitely use 10 gauge wire for the feed from the solenoid.  I'd look at the gauge of the factory wiring too though.
 

Ya know, every time I read through one of these electric fan threads, I'm reminded of all the trouble I went through with mine. I tried 3 or 4 different set ups, and the ones that worked were too loud and ugly, and the neat installation just wouldn't cool enough. Since going to the fixed blade with fan clutch, custom fitted shroud, 30% higher flow waterpump I have had zero issues with engine temperature. I get caught in traffic in over 90 degree heat, even sitting and idiling for long periods and the temp guage stays right at 190 degrees. Although I do kinda regret removing the A/C that the car originally came with.