I have a 2,000 Ford Contour dual fan set-up. It is a single speed system. I was considering using a relay pack that Volvo used to control their 2 speed fans. It has a lead for low and high speeds. When high speed is activated, low is shut off. Since my fans each only have one + lead, I would have to connect the low and high lead to each of the single + leads on the fans. You see what I'm getting at.

If low speed is activated, it will send current back through the high speed lead to the relay. Isn't that a problem? Thanks.

 

Your fans are single speed, if you had two speed fans they would be three wire. Are you trying to run one fan on low speed and both on high speed? There is a way to make this work, just let me know what your plan is.

 

Hey gashog! Yeah, that's right. They're single speed. There is no divider between the fans on the shroud to the radiator, so they can only be used together without recycling air from the engine compartment. Ford made this system 2 speeds by running 'low' through a resistor, and high by giving them full juice. But, either way, they drew the same amps, so I did away with the resistor. The issue is that regardless of where I connect my MSD box, regardless of where I connect the fan lead, when the fans kick in the ignition hesitates or sputters. That is why I'd like to use the Volvo relay pack that is designed to be used to control a two speed fan--shutting down low when high kicks in.

But I would have to run low and high leads into a single fan + lead. That means that when low is active the current is flowing back up the high speed lead to the relay. Is that a problem? That circuit is closed. Input?

I like the volvo relay pack because it's $15 in the junkyard and I can carry a spare. But, I may have to get one of the soft start controllers ... for ten times the price. I just hate those because if they fail you walk. Kevin.

 

The low speed on the relay should go open when you high speed circuit shuts. I am not familiar with the Volvo relay. I would assume it's a standard SPDT with a temp switch that controls high and low? If it stays open when switching between high and low just parallel the wiring. If not then a 30amp diode on each fan would work.

 

I would find the specs on your fans and the specs on the Volvo relay, hopefully they are not too large for the Volvo relay to handle.

Do you have A/C? You will have to tie in the clutch circuit to your fan circuit if you have A/C and it's working. If you forget this there will be a big boom under the hood. Ask me how I know this.

 

That's about what I thought. Thanks. Any idea where I can find such a diode? I checked Amazon and ebay.

 

A diode to handle such large currents is going to need a heatsink. Do you know the approx amp draw of your fans? I would guess at least 30 amps or higher reading your story about the ignition circuit not liking it. Here is a diode that can handle 40 amps. Also the diode is going to present a .7v voltage drop to the fans.

Here's one on Amazon.

 

I searched around online and found some guys using the Contour fans with the Volvo controller/relays in the AMC forum. They show that they have it wired so the low setting is routed through the oem resistor. That doesn't make sense to me. Ford installed that to create low and high speeds for the air conditioning. The Volvo controller already has a low and high speed circuit, so they are doing a double low speed. I'd be surprised if they don't burn out their fan motors using such a low amount of juice.

I am going to try it without the resistor and see what happens.

 

It appears you may not understand electricity and how it works...

In low speed operation, the Conturd fans, wired in parallel, get their power through a series resistor that reduces the current available to the electric motors which reduces their operating speed. In the high speed mode, the low speed resistor is simply bypassed and full battery power is applied to the motors causing them to run at full speed. The addition of the series resistor drops current proportionally with its value relative to the that of the motors (Kirchoff's Law and Ohm's Law both apply). Your earlier assertion that the motors draw the same current in both low and high speed modes cannot be correct.

High/low speed operation is controlled by the programming in the PCM based on operating and demand parameters.

 

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I think that before you tell someone that they don't understand electricity and how it works YOU should understand what it is they're talking about. I was not talking about the oem Contour fans and their system. But thank you for telling me the obvious that I already knew. I was talking about using Contour fans in another vehicle and controlled with a Volvo relay pack, triggered by a bmw thermo switch.

 

How do you wish the fans to operate when it's all together? I was looking at a volvo relay setup here. https://www.therangerstation.com/tec...tric_fan.shtml

From what I am getting from that article, the volvo relay is just two separate relays made together in the same package. In the article they are using a dual temp switch, one side of the switch activates one side of the volvo relay, the other side of the temp switch activates the other side of the relay.

Since you have single speed fans, you are stuck with one single speed, one function, on or off. So you all you need is one relay. One side of the volvo relay is all you need if it will handle both your fans. You could hook your temp switch to R2, and then hook both fans to C2. Or hook the temp switch to R1 and hook both fans to C1. The way the volvo relay is wired internally, you can't use both R1 and R2 at the same time or with a dual temp switch.

 

The Volvo relay does not drop the voltage. It is equivalent to two relays but packed as one. It is popular because it is robust and it is set up to only power the low OR high.

I feel like you have something else causing a problem. Your fans should not cause a voltage drop that affects the MSD ignition.

Are your fan powered straight from the battery? Where does you MSD pull it's power? How old is your battery? What size is your alternator?

 

If he had a small 16 gauge wire feeding the ignition and trying to feed the fans from the same wire, I could see where it would cause problems with the ignition.