1997+ Electric Fan Override Switch

[Mudderoy]

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

[PolarXJ]

Are you doing this so you can turn it on when you want to or off when doing water crossings?

[Mudderoy]

Are you doing this so you can turn it on when you want to or off when doing water crossings?

It isn't set up that way (yet at least). The reason it was done was purely for more control over the cooling system.

[4x4Dalton]

And has it helped your heating issues Tony?

[Mudderoy]

And has it helped your heating issues Tony?

Unfortunatly my running hot issues are on the highway not in stop and go traffic, idle, or even off road.

[4x4Dalton]

Have a stupid question then. Could your fins on rad be bent to the point that its causing the highway speed overheating issue?

[Mudderoy]

Have a stupid question then. Could your fins on rad be bent to the point that its causing the highway speed overheating issue?

I guess it's possible, however the problem occured with the two-row all metal and the three-row all metal.

[4x4Dalton]

Hey Tony ya may have already seen this but thought maybe there was some helpful info in there for ya.
http://www.jeepforum.com/forum/f310/1999-jeep-grand-cherokee-overheating-highway-speeds-1135518/

[thekevin]

I did this on my 01 and I leave my fan running all the time in stop and go traffic when it's warm enough outside to run my a/c. From what I can tell all it does it keep it from getting up to the point to where it kicks it on automatically. It still runs pretty hot.

[DeftwillP]

I take it that this doesn't cause any CEL?

[modestmar00xj]

here a random idea/thought? has anybody did any reasearch in using a bigger radiator, finding a compatable one from another car, or building/modifying the stock one? Because i have the same overheating trouble sometimes in stop/go traffic!

[Mudderoy]

here a random idea/thought? has anybody did any reasearch in using a bigger radiator, finding a compatable one from another car, or building/modifying the stock one? Because i have the same overheating trouble sometimes in stop/go traffic!

Well I have a 3 core in mine, technically that makes it bigger.

[PolarXJ]

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

Sorry don't want to highjack the thread, but where did you get those switches with the different symbols for your fan, etc..? PM me if you don't want it in the thread, thanks.

[Mudderoy]

Sorry don't want to highjack the thread, but where did you get those switches with the different symbols for your fan, etc..? PM me if you don't want it in the thread, thanks.

Crap! I thought I had it in the thread...

:link: (http://www.oly4x4.com/viewparts.php?mfgid=334200&catid=1269960&tc=7)

I like them. They are the same type and size as the ARB switches (at least that is my understanding)

[PolarXJ]

Thanks for the link :thumbsup:

[Brasscatz]

I'm wanting to do this since my new position requires me to drive a lot and my temps are reaching 227* in stop'n'go traffic and it's not even HOT outside yet! I'm not very good with wiring, so I'm having a little trouble figuring out your diagram and writeup. If I'm reading correctly though, I'm going to need a relay (amps?), I already have a spare switch, and one of those helpful relay connectors (optional, but nice to have). I'm kinda lost from there though.

[Mudderoy]

I'm wanting to do this since my new position requires me to drive a lot and my temps are reaching 227* in stop'n'go traffic and it's not even HOT outside yet! I'm not very good with wiring, so I'm having a little trouble figuring out your diagram and writeup. If I'm reading correctly though, I'm going to need a relay (amps?), I already have a spare switch, and one of those helpful relay connectors (optional, but nice to have). I'm kinda lost from there though.

I think the fan pulls 9 amps on start up, if so, 15 amp relay, but I think the standard automotive relay you get from autoparts for $8 is 30 amp.

[Brasscatz]

Ok, so the relay diagram is depicting the new relay that you added to the system. I don't understand the squiggle between 86 and 85. I think I figured out the lines under the switch and the lines coming from 30 are grounds. I don't understand the line between 87a and 30... do you bridge those terminals? You stated to just run a line to the positive 12volt side of your battery, I don't understand from where. From the switch? Also, the DB/WT wire does come into play from terminal 86? I apologize in advance for my ineptness to electrical :D

[Mudderoy]

Ok, so the relay diagram is depicting the new relay that you added to the system. I don't understand the squiggle between 86 and 85. I think I figured out the lines under the switch and the lines coming from 30 are grounds. I don't understand the line between 87a and 30... do you bridge those terminals? You stated to just run a line to the positive 12volt side of your battery, I don't understand from where. From the switch? Also, the DB/WT wire does come into play from terminal 86? I apologize in advance for my ineptness to electrical :D

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

That's inside the relay. You have to know your relay so you can make sure you're hooking it up right. The squiggly thing is a electro magnet. When it energizes it make the switch, the line at an angle above, switch.

[Brasscatz]

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

That's inside the relay. You have to know your relay so you can make sure you're hooking it up right. The squiggly thing is a electro magnet. When it energizes it make the switch, the line at an angle above, switch.

Ok, that makes sense, thanks. So about the other parts? I don't understand the line between 87a and 30... do you bridge those terminals?

You stated to just run a line to the positive 12volt side of your battery, I don't understand from where. From the switch?

Also, the DB/WT wire does come into play from terminal 86?

[Mudderoy]

Ok, that makes sense, thanks. So about the other parts? I don't understand the line between 87a and 30... do you bridge those terminals?

You stated to just run a line to the positive 12volt side of your battery, I don't understand from where. From the switch?

Also, the DB/WT wire does come into play from terminal 86?

The square represents the outside of the relay. Everything inside the square are the internal parts of the relay. If you look at the relay it will have metal tabs, or contacts. In the plastic the will have numbers, or numbers and a letter next to each one. That corresponds to the numbers and or numbers and letter on the diagram.

A dot with a line is a switch, internal to the relay in this case. I called it an angled line in the prior post.

Check this out...

http://www.pcbheaven.com/wikipages/How_Relays_Work/

[Carves]

... and this one.

Its even got some clicky click, interactive features, to play with.

http://www.bcae1.com/relays.htm#demo

[Brasscatz]

I must be more tired than I thought lately... lol. This new job is really draining me. I have a very basic understanding of relays and how they work, but for some reason it wasn't translating from diagram to actual relay for me. I think I've got what you were talking about... and I had missed the line calling it an angled line. Oy, sorry for all the confusion fellers. :D One last question for now, and I'm afraid to ask because I'm sure it's either a very obvious answer or it's already in a post that I didn't see when I re-skimmed it..... on the switch, I'll run the ground and a power, just opposite than usual because we are basically closing a ground circuit rather than a power circuit, correct?

[Brasscatz]

Help!!! Trying to get this finished tonight and it's not working! Here's my thread with what I've got so far http://www.xjtalk.com/showthread.php?p=147178#post147178