Aux fan controller wiring
05-23-2016, 09:33 PM
#1
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Year: 1998
Model: Cherokee (XJ)
Engine: 4.0
Aux fan controller wiring
I'd posted a reply to a thread in the modified Cherokee forum a while ago but got no response, so I figured I'd try here. It's more of an electrical question anyway. Bottom line is I'd like to wire up a switch so I can manually turn on my aux cooling fan, but I have heard people get problems with CELs and that sort of thing. This guy posts a quick workaround that I plan to try, but I had a concern about operating it when the PCM had the fan turned on (coolant >218* or A/C compressor running) and the manual switch was also on. See below. Will this work, or will I fry my fan or something else?
I'm still not sure why you guys screw around with trying to trick the PCM and tripping CELs and stuff.
Its simple...
Get a switch and relay. Wire the switch to trip the relay and splice it in to the hot wire on the fan right at the fan itself. The PCM will still work to turn it on when it is hot or the ac requires, but your switch will allow you to run the fan when you want. If you power the switch to trip the relay with a "always hot" wire, you can run the fan with the engine off for a few minutes to keep air flowing over the motor. Works great with hood vents.
If you power the switch with an ignition controlled power source, you wont have to worry about forgetting to turn it off.
This works with ALL model years and I have yet to see it trigger a CEl.
LEAVE the PCM ALONE!
Its simple...
Get a switch and relay. Wire the switch to trip the relay and splice it in to the hot wire on the fan right at the fan itself. The PCM will still work to turn it on when it is hot or the ac requires, but your switch will allow you to run the fan when you want. If you power the switch to trip the relay with a "always hot" wire, you can run the fan with the engine off for a few minutes to keep air flowing over the motor. Works great with hood vents.
If you power the switch with an ignition controlled power source, you wont have to worry about forgetting to turn it off.
This works with ALL model years and I have yet to see it trigger a CEl.
LEAVE the PCM ALONE!
Pardon me for asking a stupid question, but is there a concern about having two 12v sources going to the fan at the same time when the switch is on also with the A/C or 218*+? Does this double the voltage, or is it not an issue? With the hot weather approaching, I'd like to wire up my aux fan switch, and I don't want to mess with CELs and that sort of thing.
05-23-2016, 10:02 PM
#2
CF Veteran
Fan wiring
Originally Posted by Jamison 
I'm still not sure why you guys screw around with trying to trick the PCM and tripping CELs and stuff.
Its simple...
Get a switch and relay. Wire the switch to trip the relay and splice it in to the hot wire on the fan right at the fan itself. The PCM will still work to turn it on when it is hot or the ac requires, but your switch will allow you to run the fan when you want. If you power the switch to trip the relay with a "always hot" wire, you can run the fan with the engine off for a few minutes to keep air flowing over the motor. Works great with hood vents.
If you power the switch with an ignition controlled power source, you wont have to worry about forgetting to turn it off.
This works with ALL model years and I have yet to see it trigger a CEl.
LEAVE the PCM ALONE!
I have a'91 mine stopped working and I decided to just wire it this way, I actually don't have it wired through the pcm any more but will some day fix that. Just have to remember to turn it on when ever I am pushing it hard. So far I have not had any issues with my engine light. (knock on wood) But I also think the cel problem is on 95 and newer.
I'm still not sure why you guys screw around with trying to trick the PCM and tripping CELs and stuff.Its simple...
Get a switch and relay. Wire the switch to trip the relay and splice it in to the hot wire on the fan right at the fan itself. The PCM will still work to turn it on when it is hot or the ac requires, but your switch will allow you to run the fan when you want. If you power the switch to trip the relay with a "always hot" wire, you can run the fan with the engine off for a few minutes to keep air flowing over the motor. Works great with hood vents.
If you power the switch with an ignition controlled power source, you wont have to worry about forgetting to turn it off.
This works with ALL model years and I have yet to see it trigger a CEl.
LEAVE the PCM ALONE!
I have a'91 mine stopped working and I decided to just wire it this way, I actually don't have it wired through the pcm any more but will some day fix that. Just have to remember to turn it on when ever I am pushing it hard. So far I have not had any issues with my engine light. (knock on wood) But I also think the cel problem is on 95 and newer.
Last edited by JandDGreens; 05-23-2016 at 10:04 PM.
05-25-2016, 05:15 AM
#3
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Year: 2000
Model: Cherokee
Engine: 4.0L I6
Assuming you're 97+ this might help you out.
https://www.youtube.com/watch?v=-P2c...tailpage#t=387
We also covered extended idle if it suits your fancy.
https://www.youtube.com/watch?v=-P2c...tailpage#t=387
We also covered extended idle if it suits your fancy.
05-25-2016, 09:31 PM
#4
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Year: 1994
Model: Cherokee
Engine: 4.0 H.O. K&N, Borla headers, custom down pipe, magnaflow hi-flo cat, flowmaster to turn down tip
I have a secondary fan controller switch, and i wired it in to the power kick on wire directly to the fan. I first let the computer trip the fan at ~220* and then turned it on. Measured the voltage, no spike, no jump, everything ran at the same voltage no matter which, if not both power sources were activated. Hope this helps.
05-26-2016, 03:03 PM
#5
Senior Member
I have my e-fan on a push button timer--no issues with any CEL's or any other issues. If you are interested I can find a link to where I got the info from.
05-30-2016, 05:47 PM
#6
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Could someone please post the link to hard wiring in the switch to the E/fan, I am not that savvy, and will probably burn my jeep to the ground without proper assistance.
Thx in advance for any and all help.
Thx in advance for any and all help.
05-30-2016, 06:22 PM
#7
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Year: 2000
Model: Cherokee
Engine: 4.0L
Im using a pos old iphone so I cant really do much. if nobody gets back to you I could try to find the links and diagrams I used but may take me a few days.
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