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Old 06-27-2012, 10:40 PM
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Help - Recreating Fan Wiring Diagram Using Derale Controller & GM Stock System

Hi everyone,

I was hoping I could tap into some electrically savvy hotrodders for this electrical issue. Recently, Derale redesigned one of their Adjustable Electrical Fan Controllers. They switched the unit from being a POSITIVE switching circuit to a NEGATIVE switching circuit. One of the camaro enthusiasts who is no longer with us, designed a wiring schematic that allowed the GM stock fan controller to work in conjunction with the Derale system. Recently, Derale changed the circuit and well a bunch of us who have burned out relays now need a new schematic.

The problem as we see it so far. The GM Stock cooling system is always grounded. The ECM grounds the Primary Fan Relay, which energizes the relay, which then closes the circuit sending power from the battery to the primary fan. The Derale system now wants us to hard wire 1 wire to the positive of the battery, and the negative grounding relay to the negative. In effect, I would have to cut the GM ground wire (disabling it) and run the derale (-) to the the fan in addition to running battery (+). The situation is somewhat complex but I am sure someone with electrical knowledge has a better idea.

Below is the original How-To tutorial from gmtips.com:

Tech Tips
Dual Circuit Cooling Fan System

Installation of the Derale Adjustable Fan Switch (DAFS)

If you are here you already know why. You want to have more control of your engine temperature since the factory GM default cooling fan temperature set points are potentially to high resulting in overheating and power loss in severely hot climates and under AC operation.

As suggested by 3rd Gen Member "Willie" in his article http://www.thirdgen.org/newdesign/te...ooling Systems ideally there would be a couple of times you might want to revert to the stock GM settings:

1. During vehicle emissions testing.

2. During extreme cold weather conditions for purposes of heater and defrost operations.

Additionally, if you could leave the GM fan system intact, it would provide a nice backup in case of DAFS component failure.

Please read definitions under Auto Electric Basics to gain a better understanding of the terminology I have used in this article. Also, you might consider doing this mod in conjunction with other Cooling System Mods recommended.

Here is a listing of the parts you will need:

Derale Adjustable Fan Switch (Part #16759)
SPST 30 Amp Relay that is Normally Closed
SPDT 30 amp switch
Extra Wires (match gauge and color to Derale unit)
Ring connectors (for 12-14 and 16-18 gauge wire) 3/8" and 1/2"
Heat shrink tubing.
Solder gun and solder.
GM plastic split conduit (Optional)



To the left of the gray centerline is the stock GM system, to the right is the DAFS and its component additions. The beauty of this system is that your stock GM system will still be functional and you will be able to change between the two cooling systems at the flip of a switch.

Derale suggests that it replace the stock GM system and use the following wiring instructions:
Red Wire to attach to the positive (+) side of battery.
Orange Wire to attach to positive fan lead.
Yellow Wire to attach to a switched ignition source (Hot in Run).
Green Wire to attach to positive wire on AC clutch.
Black Wire to attach to good chassis ground.

We won't do that.

We will alter this configuration as follows:
Red Wire taps into GM Hi-Amp hot wire from fusible link.
Orange Wire taps into GM Hi-Amp B/R (+) wire running to fan from relay.
Yellow Wire taps into GM hot in run wire coming from 20 Amp source from fuse box.
Green Wire attaches to one of the toggle switch post.
Black Wire attaches to the out side of the hi-amp output of the relay.

We also add:
Blue Wire (you choose color) from switch terminal to positive side of lo-amp relay input.
Red Wire (you choose color) noted on right side of graphic goes to fuse box and supplies common (+) lo-amp voltage to toggle switch.

Please note: you may choose Hot in Run or Hot all Times, but be cautioned in Hot all Times your fan can run with car switched off. The only reason for providing this option is for drag racing purposes to cool off engine in between runs.

It is recommended you hook this lead to a Hot in Run source to prevent unexpected battery drain.

Theory of Operation

Since the GM system kicks on at about 234 and the DAFS is factory pre-set at 170 (totally adjustable ) the best that could happen is the GM system never again kicks on. It is a moot point that the GM fan system is concurrently hooked up because the DAFS will over ride it and control when the fan operates.

Only in the event of DAFS failure or by your choice (manual over ride switch) would the GM system be deployed. Additionally by using a normally closed relay and a toggle with the middle position (off) the DAFS is the default system and it is with no current running through the switch and the new relay not energized.

This should provide a more stable, dependable, safer circuit. The relay requires a (+) & (-) lo-amp source to energize, and when it does it breaks ground to the DAFS disabling it and returning your system to the stock GM operation.

Lets look at what happens when we toggle between different switch positions:

Function 1: Flip the switch one way (red wire):

Power from a fuse box source goes into the switch, out of the switch via the blue wire, into the positive lo-amp input of the relay, energizing solenoid, breaking ground (disabling) the DAFS for stock GM operation
.
Function 2: Flip the switch the other way (same red wire):
Lo-amp, (+) power is routed to green wire of DAFS which results in manual fan operation mode. Since the GM system was never disabled your AC clutch operation works as it always did, allowing you to use the AC operation green wire of the DAFS for manual fan control.

Function 3: Middle toggle:
Relay de-energizes and closes (switch current is off), therefore, the
DAFS takes control of the cooling fan.

That's all there is to it!

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Old 06-28-2012, 06:49 PM
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You are way overthinking this problem.
If you use the grounding path the derale controller gives to command fan on and just splice it to the ground point for the stock GM cooling system RELAY ground path, it will function properly.
The same wire that goes to the ECM from the ground side of the GM RELAY itself is where you want the derale ground to go. It wont matter if the ECM grounds the relay at 234 or the derale controller grounds it at whateverlower temp you set it too. As long as One or the OTHER grounds that circuit, the fan will run. This also eliminates the human error involved with flipping a switch if one system fails. If the Derale system fails to ground the wire to the fan relay, the GM system will act like a redundant or fail safe to turn the fan on. Simple.
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Old 06-28-2012, 06:58 PM
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The red wire on the NEW derale diagram is the ground path, which is counter intuitive, but a ground path nonetheless. Using the first diagram for the GM part of the circuit, eliminate the OLD derale part of the diagram and using the red(counterintuitive) wire from the derale relay of the new diagram, splice it to the ground side of the cooling fan relay coil.Like I said which ever one grounds the circuit , runs the fan. Leaving the factory harness totally intact.
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Old 06-28-2012, 07:09 PM
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[IMG]my pictures derale.gif[/IMG]
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Old 06-29-2012, 04:03 AM
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X2 with Latech
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Old 06-29-2012, 07:43 AM
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Would grounding that wire give a false signal to the ECM ?? What I mean is that the ECM may see the the - input as a short, and put up a code.
Just my 2 cents
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Old 06-29-2012, 03:44 PM
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Quote:
Originally Posted by hemi43 View Post
Would grounding that wire give a false signal to the ECM ?? What I mean is that the ECM may see the the - input as a short, and put up a code.
Just my 2 cents
Thats is a great question. It may, and it may not. I am leaning towards not. There is one way to know for sure.
If it did generate a code, it would not be a "A" priority code, most likely would be a "C" or "D" priority, which would not illuminate the Engine light.
Great question. It would be handy to know the answer for sure.
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Old 07-01-2012, 08:57 AM
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try this

Hi Fcastro

I think I see the problem.You are breaking ground to control unit.Sorry this is a big no,no .Your temp sensor may be backfeeding a ground to the control and possibly causing damage.I would put that swtich in the power feed circut.Center post feed power,post1 control unit,post2 control unit and green wire.Then add a wire from ac cluch + to post2.Then you dont need a relay.

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Old 07-08-2012, 05:53 PM
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When I originally built my T-Bucket, I used the first version of the DeRale fan controller. That controller failed after two years and I replaced it with what I thought was the same controller, only to find the same issue you describe (redesigned to switch the ground side). Okay, no problem, installed the new version and move on. Controller failed again this week after be used in the car for 3 years. Both times, it appears the controller got hot and the relay had to be pried out of the controller's base. I'm running a single 2600 cfm fan which should be well within the capability of this unit. I've also installed an identical replacement fan thnking that was an issue, however unless both fans are bad it looks like the DeRale controller is 0-2 for me.

I'm thinking of trying the Painless unit (#30114 I believe) which switches the positive side of the circuit, so I'll be doing a little changing in the circuit again but it's not a big deal.
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Old 07-08-2012, 06:39 PM
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If you wire the derale ground circuit to the OE relay coil ground as I described, it will prolong the life of the controller.
If you dont have the same setup as the OP just add a relay for the fan circuit, prefferably a 40 amp bosch, and use the derale controller relay to activate the bosch relay COIL, that way the derale control will last as it is only handling a small amount of current to run the Bosch relay which is handling the Load. And the bosch job is dispensable, or at least more so as it is quite a bit cheaper than the derale unit.
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Old 07-08-2012, 06:42 PM
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Quote:
Originally Posted by LATECH View Post
[IMG]my pictures derale.gif[/IMG]
Same circuit theory as pictured in post above. Just erase the ECM from the diagram.
The red wire is the grounding wire (counterintuitive) from the derale controller.
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Old 07-08-2012, 07:51 PM
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I dunno if this helps or not, but Four Seasons has a similar fan controller.
Sorry, I'm not sure how it's wired.

[Four Seasons 2011 Illustrated Guide] See page 220.

PN is 35879.
OE (GM) #19189400
More info from Four Seasons (you'll need to select the "Part Number" tab and enter "35879") including this Warning

Last edited by 66GMC; 07-08-2012 at 07:59 PM. Reason: Clarified Links
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Old 07-08-2012, 08:27 PM
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Quote:
Originally Posted by LATECH View Post
If you wire the derale ground circuit to the OE relay coil ground as I described, it will prolong the life of the controller.
If you dont have the same setup as the OP just add a relay for the fan circuit, prefferably a 40 amp bosch, and use the derale controller relay to activate the bosch relay COIL, that way the derale control will last as it is only handling a small amount of current to run the Bosch relay which is handling the Load. And the bosch job is dispensable, or at least more so as it is quite a bit cheaper than the derale unit.
Now that's a reasonable idea. Just might have the controller relay trigger a pair of relays in parallel to help prolong the life of the secondary circuit and provide a backup. Might be a bit of overkill, but I hate it when you see the temp a little above normal and realize your fan won't come on.

Thanks for the suggestion.
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Old 07-09-2012, 03:47 AM
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I use the Dakota Digital controller, so far so good. I got it party due to some of it;s features and ease of install.
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Old 07-12-2012, 11:07 PM
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Thanks so much for all the replies so far guys. I was wondering why I hadn't seen any replies. Apparently the server isn't emailing me notifications even though I am subscribed to the thread.

LATECH,
My first thought was to use the derale grounding wire to send a ground signal to the wire between the ECM and GM relay. 2 problems, 1 I don't want to damage the ecm, 2 if the GM relay is failing or fails in the future the whole system is dead in the water.

LATECH, do you think you could just quick sketch up the bosch setup you just mentioned? It sounds promising.

2x4 Barrels,
Wow yes the original system as it was designed breaks the ground of the Derale system. Do you think you could explain a bit more? That totally sucks if breaking the ground is causing the Derale unit to fail.

cucumber1949,
I have read a few other forums where people also mention derale controllers failing, and there not cheap! the fact that they redesigned the fan controller had me thinking poor quality. My original controller lasted a few years and failed!
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