Fan override switch 97+ models

[XJJack]

No, your just not understanding what I said, if you look at that last digram. Just think of the relay and look at term 30 87 and 87A, cut the feed to the fan and route to 87A then ether ground or hot, witch ever one you are interupting to 87 then the fan to 30 and you are done, no relay to go bad.

 

[Red97XJ]

OK, I thought I was fairly good at electrical.... but I can't get this one.

so who here has it right? XJjack or DotheDew?

I will decipher how to actually do it once we (you guys) hash out the best way to do it!!!


Thanks,
Jason

 

[Eagle]

Dothe Dew's diagram is incorrect.

The aux fan on the new models is controlled by the ECU, and the ECU (or PCM) does power the fan by activating a relay. That much is correct. According to the 2000 FSM, though, the relay (which is in the power distribution center) does not have the terminals numbered like a standard relay. The FSM uses numbers D10, D11, D13 and D14. These would correspond in the diagram above to 85, 86, 87 and 30. 87A (or the equivalent, which is not numbered in the FSM) is not connected to anything.

PCM to D13 (85 or 86) is an 18 gage wire, dark blue w/purple (pink?) trace. The other side of that circuit is D11 (86 or 85) and goes to ground.

Battery in for the power side of the relay goes to D10, which corresponds to 30 on a standard relay. Power out to the fan is D14, which would be 87 on a standard relay.

Folks, this setup is NOT negative switched. There's a 12 gauge light blue wire from the relay to the fan, and from the fan there's a 12-gage black wire directly to ground.

This means that if you wire in a single pole toggle switch to override the PCM and turn on the relay ... you will be tapping in between the relay and the PCM, and that means you would be back-feeding 12 volts into the PCM. Whether or not this would have any effect on the PCM I don't have a clue. Don't want to find out the hard way.

Simple solution: As noted, a SPDT toggle switch (single pole, double throw).

Cut the wire from the PCM to the relay. Connect the middle (common) terminal on the SPDT switch to the wire leading to the relay from the cut. Connect one of the switched terminals on the switch to the wire leading back to the PCM. Connect the other wire to a fused 12-volt source. Switch in position A gives you stock operation, switch in position B isolates the fan relay from the PCM and uses direct 12-volts to activate the relay. No back-feed.

 

[kraziexj]

on my 98 I took a voltage tester and poked around with the relay that controls the fan. I found that if i grounded one the of the wires the fan turned on and the others remained the same. So i just ran a wire from there to a switch and grounded it. it has worked flawlessly for over a year, except the fact that the check engine light is always on.......

 

[Purple]

Purple: jxj,but if you did that, and battery power is connected to the fan, just above the plug, doesnt that transfer power to the harness, when you turn it on? What i wanted to do is install two relays in that circuit, one for the fan, and the second one would disconnect the stock fan wiring...

Isn't that the same thing as Eagle said?
am i missing something or what? can someone draw a diagram for 97+ and get this over with?

 

[TacticalFats]

Help.

Bump....

I tried this last night.

As Eagle said, I put a switch SPDT switch in, exactly as described in his post (center to the relay, one wire to the PCM, one to 12V).

I throw the switch, nothing. I turn the switch off, the fan spins about one time. Ok, that's weird. I turn the a/c on, it works fine (of course it only cyled for about 2 seconds because it was freezing). I throw the switch, CEL light.

Great; I turn the car off, unhook and re-set the battery. I get in the car, before turning the switch, and THE FAN COMES ON and the ABS light GLOWS dimly.

WTF?!?!?!

 

[Gridikal]

Once again mine works fine for my 97.


Thats all.

 

[Roxtar]

Dude, what is it you want to do?
Turn it on or turn it off?
There's really no reason to turn it on early because you want the engine to run at 210* so there is no reason to turn it on before the computer does.
If you want to be able to shut it off for water crossings, again, very little reason to do this because the mech fan will blow far more water than the electric does, just put a switch in the line running to the fan.

 

[TacticalFats]

I want to be able to turn it on at will, for a number of reasons.

I re-wired it to be fed off it's own separate circuit. It's now exactly as DoTheDew's diagram illustrates. And it works fine!

 

[robsewter]

I recently bought the kit from xj armor for my 99 and the plugs on my fan are square, his kit has round ones. Of course after months of sending email i have given up. What im looking to do is find plugs that are identical to my current ones on my jeep and put them in place of the ones he has on the kit. Does anyone know where I can find these plugs?

 

[GirlScout1]

My E fan didn't work for the past 3 years and I finally just said screw it and put in a Hayes one. I think I paid $60 for it and put it on a switch. Works great though I don't use it very often unless i'm out wheeling or stuck in grid lock. I also leave my hood popped too on the trail to help keep the heat down...unless i'm cooking Hot Pockets of course.

 

[bobb]

Just pull the A/C clutch relay. When you want the aux fan on, put the heater control switch in defrost.

 

[javik]

I put a brass t where the regular thermostat is and put a much lower tstat on the other end of the t and wired that through a relay to run the fan. You can do it out of the bus, or battery direct. power relay in, power out of relay to fan hot, mine is jumpered. tstat switch in and out. Done. Im no electircal wizard, but it seems to work fine. My EE budy helped me do it. I think that setup should work for a 97+. I have it on a 91 and it works great That way you dont forget about turning it on. I think the fan is always grounded and is not tuned on by the car pcm pulling it down to ground. Maybee this will help, or maybe im an idiot, or both.

 

[Red97XJ]

Just pull the A/C clutch relay. When you want the aux fan on, put the heater control switch in defrost.

OK, this seems like a REALLY easy quick offroad fix that sounds like it would work great! Is there any negative effects to this? What about the A/C system.... is there anything else it would effect?

Sorry for the dumb Q's, this just seems super easy to do before a day on the trail.

 

[TheHighHeat]

sorry to drag up an old post, but no need to start a new one, I've been wanting to do this on my 2000 because after I turn my Jeep off it gets too hot, so after messing around with a voltmeter here's what I got, I have a black wire and a green wire coming from the fan into the connector, out of the second connector a blue and black wire come out, the black wires are ground and the green/blue wires are power, when the fan is off I get no reading from the green/blue wires and resistance on the ground, when the fan cuts on I get 12.8V on the green/blue wires and no resistance on the ground, which is all good, so my main question is, if the PDC is sending 12V to the fan would adding a switch and a relay like in the diagram below work?When it comes to the electrical I'm not the best so I wanted to get some opinions

click the photo for full size

 

[DaffyXJ]

Yep, that will work.
For ease of access you can splice into the green wire right at the fan, mount your new relay near the airbox, grab 12V B+ from the batt or PDC and run a wire across the top of the fire wall. Then inside the cab grab 12V ACC or B+ from the fuse block to the switch. So only wire that has to go through the firewall is the 12v low current to the relay.
Make sure you use 12 Gauge wire min (10 better) from batt to pin 30 and 12gauge from 87 to fan. Fan pulls up to 30 amps on start up.

 

[TheHighHeat]

After thinking about it a lot I didn't want to take the chance of sending 12V back into the PDC so I used the image that DoTheDew provided and it works great, flip the switch and the fan turns on, switch off and hte fan turns on/off when Jeep wants it to, it also doesn't do anything strange when the switch is on and the Jeep tries to turn it on, now all I need to do is a find a factory harness, the Jeep dealer only carries the entire harness from PDC to fan which doesn't include both sides, and all the junk yards here have no 97-2001 XJs or TJs, I'm shocked...