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Mudderoy
11-04-2010, 03:34 PM
http://lh4.ggpht.com/_b0ViaGso2Ko/TD5l6TPAf-I/AAAAAAAAAUw/dXRzYQf6nT4/s800/2010-07-14%2019.43.29.jpg

I have installed and tested this on a 1998 Jeep Cherokee, but based on what I have read it should work on 1997 to 2001 Jeep Cherokees. Please post your OWN findings here!

The following circuit diagram shows a standard automotive 12 volt relay.
The DB/WT stands for Dark Blue with White stripe wire, and DB/PK for Dark Blue with Pink stripe wire.
Through some experimentation I found that instead of splicing into the DB/WT wire you should run a wire to the positive side of your 12 volt car battery.

If you look closely on the back of your relay you will see the 30, 86, 85, etc...

http://xjtalk.com/images/special/auxfanbypass.jpg

You will need to find the dark blue with pink stripe wire under the hood on the driver's side of your 1997+ Jeep Cherokee.

http://lh5.ggpht.com/_b0ViaGso2Ko/TDtqkRngoJI/AAAAAAAAAUM/ZRb65auBVFo/s912/2010-07-11%2014.28.27.jpg

http://lh4.ggpht.com/_b0ViaGso2Ko/TDtq7GKgy2I/AAAAAAAAAUA/0EVgQpEmd0U/s912/2010-07-11%2014.27.51.jpg


I recommend you use a Digital Volt Meter (DVM), voltage probe etc... to verify that this is the CORRECT wire that controls your electric fan.
You will cut this wire. The DB/PK wire that goes to the PCM (Computer) will be attached to the relay 85 terminal. The other half of the DB/PK wire goes to the relay 87 terminal. You can attach a ground to the body and relay terminal 30 for a ground. Now just run a line to the positive 12volt side of your battery. At this point your electric fan will work as it did before, automatically with the A/C on and when the coolant temp reaches it's pre-programmed trigger point.

Simply adding a switch between relay terminal 87 and ground will now allow you to override the PCM and turn your electric fan on. It will remain on until you turn the override switch off, or turn the ignition key to off.

I recommend a fuse between the switch and the ground. Double check, but I believe a 10 amp fuse will do. Make sure you use the proper gauge wire to handle 10 amps continuously.
http://lh3.ggpht.com/_b0ViaGso2Ko/TDtriPQfBBI/AAAAAAAAAUE/8jrSlKcX8qs/s912/2010-07-11%2014.27.19.jpg

http://lh3.ggpht.com/_b0ViaGso2Ko/TD5lz8TRXxI/AAAAAAAAAUs/Wr4cqTcPRE4/s640/2010-07-14%2019.42.41.jpg

http://lh4.ggpht.com/_b0ViaGso2Ko/TD5l6TPAf-I/AAAAAAAAAUw/dXRzYQf6nT4/s800/2010-07-14%2019.43.29.jpg

03ghosthemi
01-23-2011, 02:32 PM
Just a few questions. What did you use for the overhead pod and how did you mount it? Also where did you buy your switches?
Great write up.


Bill

Mudderoy
01-23-2011, 02:50 PM
Just a few questions. What did you use for the overhead pod and how did you mount it? Also where did you buy your switches?
Great write up.


Bill

I keep forgetting to reformat this post into an "article" form, but here's the link and will give you more information that you want. :smiley-laughing021:

:link: (http://www.xjtalk.com/showthread.php?t=2215)

Feel free to ask more questions though.

Chex_Mex
04-02-2011, 02:35 AM
very nice writeup, i'm going to try this when i get back in country. :D

Mudderoy
04-02-2011, 04:55 AM
very nice writeup, i'm going to try this when i get back in country. :D

I was just going to post, "WHERE THE HELL HAVE YOU BEEN?!?!?" but you just answered that question. :D

jccatt
04-02-2011, 04:59 AM
Mate, thats a top idea.

Marsbar
05-20-2011, 11:17 AM
Mate, thats a top idea.

Hi James, yes i finally have got myself on this great forum you've been telling me about.

Yeah the manual control of the fan is a good thing. I was having over heating probs when crawling in the bush in low range so I also fitted a 10" thermo-fan to the front of the A/C condenser on the same side as the mechanical engine fan.

I've set the fans to operate a bit different. With the manual overide switch turned off the factory electric fan operates as normal, but when I turn the manual overide switch on, the factory & extra 10" fan come on together......but this is where it gets tricky, coz i have build a timer that comes on when I turn the Ignition off & runs both fans for 4mins to help get the temperature down. After the timer shuts down there isn't any current draw so doesn't flatten the batteries

95 Cherokee
01-28-2012, 01:23 AM
Would really like to hear and see if possible more about the electric fan mounted on / in front of belt driven fan ??

4.3LXJ
01-29-2012, 09:39 AM
Would really like to hear and see if possible more about the electric fan mounted on / in front of belt driven fan ??

Try this one:

http://www.xjtalk.com/showthread.php?t=7999

Marsbar
02-01-2012, 09:04 AM
Would really like to hear and see if possible more about the electric fan mounted on / in front of belt driven fan ??

Hi Bob,

I'll get some pic's happening over the weekend for you with the addition of the thermo fan. It isn't rocket science as all I've done is to fit it in front of the A/C Condenser (i used a slimline 10" fan coz on my 2001 update there isn't much room between the condensor & back of the grill) but I have first replaced the OEM auto cooler & fitted a V8 Trans cooler that fits neatly on the front of the A/C condenser & gets assisted air flow from the factory thermo fan on the back of the radiator. By fitting a more efficient transmission cooler it will help the gearbox cope with the slow rock crawling, low range wheeling we do with our trucks + it gave me the room on the 10" fan on the other side of the condenser.

I don't know if our Australian XJ's are the same layout for the Radiator/Air Con as your U.S. trucks & that might have an effect on how you fit it up. Our Trans cooler had the pipes/hose come thru on the RH side of the radiator & the factory cooler went across the bottom of the A/C condenser which stopped me from fitting the extra fan on the front until I converted to V8 Cooler.

I'm happy how well it turned out & it only cost me $220 including the 4min timer(I custom built it), extra relay, switch, V8 Trans Cooler & 10" thermo Fan.

Cheers,

AL

Marsbar
02-05-2012, 01:46 AM
Would really like to hear and see if possible more about the electric fan mounted on / in front of belt driven fan ??

Sorry it took so long to get 2 pic's Bob,

Chex_Mex
04-27-2012, 05:03 PM
Hey Mudderoy, quick question. when doing this mod, do you get the CEL on whenever you switch the fan on? (just checkin before i do it as i i have read some people's CEL coming on after they put on a fan override switch):bang:

Mudderoy
04-27-2012, 07:48 PM
Hey Mudderoy, quick question. when doing this mod, do you get the CEL on whenever you switch the fan on? (just checkin before i do it as i i have read some people's CEL coming on after they put on a fan override switch):bang:

I did when I first tried it, later I figured it out. I ran the 12volt line straight to the battery. No more cell code.

eking81
07-20-2012, 01:08 PM
i have a question on this . by adding a switch between the pcm and the relay and the switch being powered by straight power from the battery wouldnt you worry about power feeding back to the pcm when you turn the switch on

Mudderoy
07-20-2012, 03:37 PM
i have a question on this . by adding a switch between the pcm and the relay and the switch being powered by straight power from the battery wouldnt you worry about power feeding back to the pcm when you turn the switch on

You want 12 volts on the PCM line all the time, that's why it is connected through the coil. In fact that was why I was getting a CEL light before I moved where I was getting the 12volts from a source that wasn't always on.

dagr8tim
05-14-2014, 02:24 PM
Not to drag up and old thread, but I'm having problems wrapping my mind around the relay pinout. Here is what I got from the original post.

30 - Hot from Bat
85 - Ground
86 - From Fan (DB/PK) - Trigger/Input
87 - To PCM (DB/PK) - Output - Splice with a switch to ground for override.

Please correct me if my understanding of the pinout is incorrect. I'm considering doing some cooling maintenance this weekend and thought this might be a nice little mod/upgrade?

Also, what are your thoughts about a fuse between the relay and the override switch in the cab?

Mudderoy
05-14-2014, 10:11 PM
Not to drag up and old thread, but I'm having problems wrapping my mind around the relay pinout. Here is what I got from the original post.

30 - Hot from Bat
85 - Ground
86 - From Fan (DB/PK) - Trigger/Input
87 - To PCM (DB/PK) - Output - Splice with a switch to ground for override.

Please correct me if my understanding of the pinout is incorrect. I'm considering doing some cooling maintenance this weekend and thought this might be a nice little mod/upgrade?

Also, what are your thoughts about a fuse between the relay and the override switch in the cab?

You can try it but I what I did was in the diagram with the exception of the 12v going to the battery.

dagr8tim
05-15-2014, 10:05 AM
You can try it but I what I did was in the diagram with the exception of the 12v going to the battery.

I'm trying to duplicate your effort, and I'm better at reading it from a pinout list rather than a diagram. I'm just trying to put what you did into something that's easy for me to read/understand.

Brasscatz
05-15-2014, 07:24 PM
I did pretty much the same thing and labeled the wires so I know which is which.

I've got PCM, Battery +, Ground, and Switch.

http://i356.photobucket.com/albums/oo7/thestalliontruck/Red%20Bandit%20XJ/20140515_190356_zpsa9tij2iz.jpg (http://s356.photobucket.com/user/thestalliontruck/media/Red%20Bandit%20XJ/20140515_190356_zpsa9tij2iz.jpg.html)

http://i356.photobucket.com/albums/oo7/thestalliontruck/Red%20Bandit%20XJ/2014-05-15%2019.07.59_zpsxpovpjwz.jpg (http://s356.photobucket.com/user/thestalliontruck/media/Red%20Bandit%20XJ/2014-05-15%2019.07.59_zpsxpovpjwz.jpg.html)

http://i356.photobucket.com/albums/oo7/thestalliontruck/Red%20Bandit%20XJ/20140515_191255_zps6fqoewcb.jpg (http://s356.photobucket.com/user/thestalliontruck/media/Red%20Bandit%20XJ/20140515_191255_zps6fqoewcb.jpg.html)

http://i356.photobucket.com/albums/oo7/thestalliontruck/Red%20Bandit%20XJ/20140515_190309_zpslouct6zh.jpg (http://s356.photobucket.com/user/thestalliontruck/media/Red%20Bandit%20XJ/20140515_190309_zpslouct6zh.jpg.html)

All wired to the green switch on the bottom. I chose green because if it's getting too hot and acting like a green jeep... I gotta flip the switch :D

http://i356.photobucket.com/albums/oo7/thestalliontruck/Red%20Bandit%20XJ/20140515_191350_zpsiuubffx0.jpg (http://s356.photobucket.com/user/thestalliontruck/media/Red%20Bandit%20XJ/20140515_191350_zpsiuubffx0.jpg.html)

Mudderoy
05-16-2014, 03:11 AM
I have to wire mine back up. I melted a relay and a switch when I was being clever and hooking up the Dirt Bound Offroad 3 electric fans.

That bypass comes in handy off road.

Tobyspaw
04-19-2015, 08:51 PM
Hi James, yes i finally have got myself on this great forum you've been telling me about.

Yeah the manual control of the fan is a good thing. I was having over heating probs when crawling in the bush in low range so I also fitted a 10" thermo-fan to the front of the A/C condenser on the same side as the mechanical engine fan.

I've set the fans to operate a bit different. With the manual overide switch turned off the factory electric fan operates as normal, but when I turn the manual overide switch on, the factory & extra 10" fan come on together......but this is where it gets tricky, coz i have build a timer that comes on when I turn the Ignition off & runs both fans for 4mins to help get the temperature down. After the timer shuts down there isn't any current draw so doesn't flatten the batteries
I'd like to know how you built your timer for the cool down after ignition is shut off?

Metal Man
05-04-2015, 12:55 PM
Is there a reason you wouldn't just tap into the factory fan relay to give it either the 12v+ or ground it uses to switch phases? I've done it on GMs (third gen F bodies over heat as much as XJs LOL).

4.3LXJ
05-08-2015, 03:23 PM
On the OBDii systems you have to tap into the down stream side of the fan relay or it will give you a fan code and CEL. But remember, the fan relay comes on at 218°

Tobyspaw
06-23-2015, 01:55 PM
I did this mod and now my A/C does nt work. Mudderoy I could use some guidance.

Mudderoy
06-24-2015, 04:10 PM
I did this mod and now my A/C does nt work. Mudderoy I could use some guidance.

So doing a quick read it's the diagram at the top of the post but I ran a line straight from the positive of the battery to pin 86 of the relay.

I did that because I would get a check engine light otherwise.

As far as A/C not working, I don't know. Never had an issue with the A/C when I did this.

Also keep in mind I did this on a 1998 not a 2001. Something could be different.

Tobyspaw
06-25-2015, 04:13 AM
Got it figured out. A/C Low pressure switch . Why it decided to go out while I was doing your mod,I don't know.So dont use the blue wire with white stripe for anything?

Tobyspaw
06-25-2015, 08:28 PM
The A/C problem turned out to be the low pressure switch,I guess it went out at the same time I was working on the bypass.Blame it on Murphys law I guess. Anyway, figuring it was the overide, I undid the wiring changes. Currently I am just using a switch to ground the blue w/pink stripe wire to run the fan whenever I want. Heatsoak is my reason for doing your mod. I have a CEL,1491,don't mind the light being on for now but,I do want it to work the way you designed it. Just to be clear, are you saying that I won't be tapping into the blue with white stripe wire will not be used at all?

Mudderoy
06-26-2015, 12:48 AM
The A/C problem turned out to be the low pressure switch,I guess it went out at the same time I was working on the bypass.Blame it on Murphys law I guess. Anyway, figuring it was the overide, I undid the wiring changes. Currently I am just using a switch to ground the blue w/pink stripe wire to run the fan whenever I want. Heatsoak is my reason for doing your mod. I have a CEL,1491,don't mind the light being on for now but,I do want it to work the way you designed it. Just to be clear, are you saying that I won't be tapping into the blue with white stripe wire will not be used at all?

I got a CEL when I used that line so I tried getting my 12 volt source from the battery

Tobyspaw
06-26-2015, 08:12 AM
O.K. that's what I'll do.Thanks Mudderoy.

Tobyspaw
06-29-2015, 12:25 PM
All hooked up. Works really well.Thanks for clarifying that I do not use the blue with white stripe wire.

Tobyspaw
07-01-2015, 01:33 PM
Next will be to figure out how to add a timer.

Mudderoy
07-03-2015, 08:49 AM
Next will be to figure out how to add a timer.

Look up 555 timer projects

Or just buy something like this...

http://www.parts-express.com/velleman-k2579-universal-start-stop-timer-kit--320-184?utm_source=google&utm_medium=cpc&utm_campaign=pla

Oooo scratch that, get it here!

Amazon.com: Velleman K2579 Universal Start/Stop Timer: Industrial & Scientific@@AMEPARAM@@http://ecx.images-amazon.com/images/I/510JonZDWOL.@@AMEPARAM@@510JonZDWOL