How can I make an override switch for my electric fan?

[ch3wy099]

Hello everyone. I have a 1996 Jeep Cherokee XJ Sport, I wish to make a switch where I can override the relay and have the fan turn on when I want. Because it's really hot where I live, the truck does turn on the fan when the temperature reaches the limit but by that time it's still going up into the red and has to try and catch up. It does cool down eventually but I drive around a lot and I don't want my car to overheat. Does anyone have a diagram or explanation of how I can wire an override switch?

[nickyg]

I'm not the best to answer any wiring problems.
But might I suggest before you go too far.. Have you checked the fan clutch (the fan on the other end of the water pump). Sometimes it goes bad and don't spin fast enough.
I live in the south and don't have a problem with over heating with the stock set up.

[nickyg]

Here's quick video on how to test it.

https://www.youtube.com/watch?v=cOXcrbQRDWU

[ch3wy099]

The entire cooling system works properly. I do in fact have a new clutch fan maybe about a month old. The electric fan does come on with AC and defrosters and the predetermined temperature relay. The only problem is that when the truck relay does turn on because it's really hot outside it has to catch up and when it does start catching the gauge is in the red. I drive a lot and I don't want to take a risk of overheating because it's only getting hotter and hotter where I live.

[4.3LXJ]

The guy to ask is Mudderoy on this forum. He has done it without having a check engine light come on. If you don't do it right, you will get one

[Mudderoy]

Specifically for 97+ may or MAY NOT work on pre 97, in fact I've only done it on a 98.

http://www.xjtalk.com/showthread.php?t=5060

[ch3wy099]

Could this work with a 1996?

[Mudderoy]

Could this work with a 1996?


Specifically for 97+ may or MAY NOT work on pre 97, in fact I've only done it on a 98.

[Carves]

Hello everyone. I have a 1996 Jeep Cherokee XJ Sport, I wish to make a switch where I can override the relay and have the fan turn on when I want. Because it's really hot where I live, the truck does turn on the fan when the temperature reaches the limit but by that time it's still going up into the red and has to try and catch up. It does cool down eventually but I drive around a lot and I don't want my car to overheat. Does anyone have a diagram or explanation of how I can wire an override switch?


I would be looking for the reason for the "thermal runaway" ... rather than just bandaiding a problem ... with the switch hack.

Since you have a new fanclutch ... Some things to consider,

... Verify your running temps with something other than the dash gauge or a badly aimed IR gun.
... Maybe a partially blocked radiator ?,
... Too much eth-gly in the mix ?,


As for a fan control over-ride ......

When I thought one might be useful on mine,
... I just tapped into the Dk Bl & Pink wire at the PDC ... ran it to a switch on the dash and from the switch to a ground.

Mines got a '98 build badge, but I think thats coz it took 'em 3yrs in the factory,
... to put the hodge podge of 96/97/98 bits together .. :rolleyes: .. :D
... and so I didnt have a CEL issue when I flicked the switch to activate the fan.

Since turning it on early in various driving scenarios - that I'm fairly sure are a lot warmer, than in NJ ... didnt really make a lot of difference,
... I removed it all - years ago.

Before you start,
... Grab yourself an FSM so you can get confused reading through the wiring diagrams ... and peruse a few posts/vids about the mod.


My hack job ... In case its useful ....

Verifying I was about to play with the correct Dk Bl & Pink wire.
You dont need to cut the wire at the PCM connector. The one in the pic is a spare connector I used for the piccy.

Some have cut/piggybacked the wire there ... coz its closer to your LHD, drivers position.

http://i1143.photobucket.com/albums/n629/carves-oz/Vehicle%20Bits/Electrical/ThermoFan01_zpsec0f69e9.jpg


The piggyback off the factory connection at the relay.

http://i1143.photobucket.com/albums/n629/carves-oz/Vehicle%20Bits/Electrical/PDC20b_zps10df4770.jpg


The piggyback off the factory connection at the relay.
Dash, switch wiring included with a 12v power supply harness I fitted.
Where I decided to jam some switches.
It worked ... but wasnt nearly as useful as some of the gushing posts, on various jeep web sites/blogs suggest.

http://i1143.photobucket.com/albums/n629/carves-oz/Vehicle%20Bits/Electrical/Thermo%20Fan%2002_zpsmo5es1r5.jpg

.

[4.3LXJ]

To answer your question another way, relays are a powerful tool to make something do what you want. Most people just use them to switch a heavy load. But in the automotive world, these switches are reduced in size and made into controls for various operations. Here is one bank I made for managing two electric fans I have.

http://i649.photobucket.com/albums/uu215/warriorsuspension/2012-06-05_19-01-39_945.jpg

I don't expect you to make heads or tails of this. But it has four functions. First is to turn on my primary efan because of coolant temp. Second is to turn on both fans when the AC pump engages. Third is to turn on the secondary fan manually if needed and fourth is to turn the whole thing off when fording deep water. There are two ways to make this stuff operate in parallel. One is to operate the coil circuit in the relay with some type of switch, which is what Mudderoy did. The other way is to wire a relay parallel to the fan relay you have. That means the switched on wire is spliced into the wire that goes from your current relay to efan. That way, your efan would operate normally or you could switch it on manually. Because a relay isolates the source, neither relay would affect the other system. This would be simple to do.

[ch3wy099]

What do you mean by run a parallel relay to the electric fan?

[4.3LXJ]

You want to turn on the fan when you want right?

[Mudderoy]

I looked around on Google a bit. I couldn't find any write ups for anything but 97+ Cherokees. I just spent a couple of minutes on it though.

[ch3wy099]

You want to turn on the fan when you want right?

Yes.

[4.3LXJ]

The first thing is that an efan pulls a fair amount of current. Both NW99XJ and myself do not recommend trying to run a fan directly off a switch. You should use a relay which will handle much more current and use the switch to run the relay. Here is a thread so you can learn about relays

http://www.xjtalk.com/showthread.php?t=12182

Once you get to know about these little "remote switches" you will need to wire one in parallel to your existing fan relay in your power distribution center. You will need to find the wire that runs off the #87 terminal there and splice another wire into it from the #87 terminal from your new relay. That way the fan will operate automatically with your AC and temp controls and operate off your switch too. Neither leg will affect the other because the relays will isolate one from the other