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Electrical Guru's Please Help!

FordGuy

FordGuy

NAXJA Forum User
Location
San Clemente, CA
Yes I tried searching first! I have a 2000 XJ, I want to install a switch to override my Aux Fan. I want to do this because currently my Trans Cooler is mounted in front of the Radiator to take advantage of the Mechanical fan, Unfortunately this blocks a lot of air flow. If I move it to the other side it greatly improves the air flow and if I can override the Aux fan when Crawling it will cool the trans. My Idea is that if I tie into the ECU fan Command wire and install a Diode, and then install a switch wired after the new diode, This would be a very simple, clean way to do this instead of installing a total new relay circuit. would this cause any issues I am not counting on?
 
make sure it doesnt "bleed" back into the system, as far as I know the fan is controlled by the ECU for the high temp switch, if your putting power to that wire you may be back feeding something? also when the fan shuts off it can act as a generator.
 
when you have the switch off there is no problem, its when you turn the switch on the power will go not only to the fan but also to the ecu.
A diode will work well for this.
 
Has anyone confirmed that the computer switches the "hot" and not the "negative"??
 
RCP Phx said:
Has anyone confirmed that the computer switches the "hot" and not the "negative"??
Click to expand...

Before I wire it, I will check it. The problem is normally I would not question my wiring skills, but.. It is so much easier to do it this way, I keep asking myself, why does everyone wire in relays and crap when you can control it with one little wire. So I started thinking that I was over-looking something.
 
Once you get this done please let me know I would like to have mine done up better. I did mine for quick and derty so I could tow cross country. I Thought it would help but it didnt so I droped in a new 2 core rad and a 160 stat helped a lot. I also have been tosssing the idea on a trans cooler and would like to use my eletrict fan now to cool it after reading your post.
 
You're going to need a pretty big diode to handle the current, btw. I'd run the line from the ECM, a +12volt line, and the line to the fan to a SPDT toggle inside. Have the switch flip-flop the fan between +12volts and the ECM feed.

I've have to double check if this'll work on a 2000, but you could wire a diode and switch to tell the ECM the a/c is on (even if it isn't). That'll turn on the aux fan and kick the idle up a little as well. Same as the extended idle option on the older Renix's I think.
 
lawsoncl said:
You're going to need a pretty big diode to handle the current, btw.
Click to expand...
No he wont,he's controlling the relay ,not the motor itself!
 
RCP Phx said:
No he wont,he's controlling the relay ,not the motor itself!
Click to expand...

I just want to control the relay, just as the ECU does, Simple switch, no relay, or wasted wiring. just a small 20ga wire. Diode for no ECU feedback, Can't figure out any reason it would not be super simple compared to the hassle of installing an extra relay when the XJ has it already there.
 
As was said, the diode would prevent the feedback into the ecu, but would have to be rated to handle the current that the ecu turn-on circuit uses(it's in the mA range), so yeah a $3 part from Jameco. I'm using a 98 auto ecu at the moment and the aux fan is erratic with it sometimes being on all the time after start or never on even if it gets above 220*. If this 97 ax15 ecu that I'm about to get doesn't do any better, then I will definitely bypass the ecu to turn the fan on until I get another 96 ax15 ecu.
 
Last edited:
Hallo Jeepers.
I installed a led on the dash,to see when the auxfan is running. I jumped the wire from the fanconnector. When teh fan is not engaged and there is a lot of airflow, the fan is working as a generator. The led is glowing.
Is it possible to jumpwire the pins 30 and 87 of the auxfanrelais in the motorcomp. with a wire and switch on the dash?
Do I need thick wire and mayby a diode? Is it possible to make a little diagram of the place of the diode? Thanks:wave:
BTW it's a '92 with airco.
 
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All you need to do is install a Diode in the wire that goes from the ECU to the fan relay trigger wire, then tap into that same wire after the Diode, this will stop feedback to the ECU, and give you fan control without having to install any additional relay and wiring, just a simple switch. What I don't know yet is the which wire or positive or negative ECU trigger, need to get a wiring diagram.
 
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