Aux fan idea? help me out

[fyrfytr1717]

yeah john said that i would need some 18 guage wire and some 14 guage wire and also a 12 volt diode.

OK, so the OEM relay trigger wire is 18g and the OEM fan motor wire is 12g. Where does the 14g come in? Why do you need both, and where does the 12V diode get wired in? Just curious to see if the info he gave you jives with what I'm planning...

 

[gradon]

I've been dealing with the CEL from my manual ground switch to the relay. I was gonna try to use a diode until someone that did reported back that the PCM still throws a code. One of these days I'll rewire both fans and bump the mains up to 2awg.

 

[jeeperjohn]

I have to add that the Procomp style $20 fans are too cheap and easy of an upgrade to pass up.

All I can say is you get what you pay for. I had about 4 Hayden fans fail on me at the worst possible times and one of them nearly burned my rig up. I will never buy cheap fans again.

 

[jeeperjohn]

OK, so the OEM relay trigger wire is 18g and the OEM fan motor wire is 12g. Where does the 14g come in? Why do you need both, and where does the 12V diode get wired in? Just curious to see if the info he gave you jives with what I'm planning...

This was based on using the 18 ga wire through the switch to trigger the relay and the 10 ga wire attached to the OEM fan power wire to run the fan. The diode is installed in the OEM fan power wire to prevent voltage feedback when the fan is manually turned on.
You could also use the 18 ga wire to trigger the OEM fan relay, I'm not sure if there would be feedback issues or not (such as the A/C compressor coming on). This is why the manual mode would just use it's own power wire.

 

[winterbeater]

You shouldn't need a new power wire, because the fan is ground activated. It always gets power.

 

[fyrfytr1717]

I've been dealing with the CEL from my manual ground switch to the relay. I was gonna try to use a diode until someone that did reported back that the PCM still throws a code. One of these days I'll rewire both fans and bump the mains up to 2awg.

OK, so I guess this confirms that manually grounding the relay throws a CEL if you don't use a diode. I'd be curious to read what the person that used a diode and still got a CEL did exactly. It really seems like it should work just fine. I think I'll try wiring it up loosely and giving it a go. If it works, I'll make it permanent.

This was based on using the 18 ga wire through the switch to trigger the relay and the 10 ga wire attached to the OEM fan power wire to run the fan. The diode is installed in the OEM fan power wire to prevent voltage feedback when the fan is manually turned on.

I assume here you're talking about wiring in a relay in addition to the OEM relay. This is the route I'll go if I can't get make the OEM relay work the way I want it to. I don't think you need a diode in the OEM fan power wire though. When you manually turn the fan on (and the ECM isn't telling it to be on) the fan motor relay is in the open position so the power wire has no way to back feed that voltage. You do need to fuse the new power wire however.

 

[fyrfytr1717]

You shouldn't need a new power wire, because the fan is ground activated. It always gets power.

The fan relay is ground activated and always has power. The fan motor itself is switched on/off on the positive side of the circuit by that relay. The negative side of the circuit goes directly from the fan motor to Ground #106.

 

[hubs97xj]

OK, so I guess this confirms that manually grounding the relay throws a CEL if you don't use a diode.

Gah, big long detailed post, signed me out, post lost...

Suffice to say, I tried three different setups using a switch and relay. I either got a code with my ckts, or the fan wouldn't run when it should with the switch off. I think I overlooked a ground, but just took the ckt out and left the wiring as it was. I wanted to be able to turn the fan on whether I had the AC or defroster running or not, with no codes under any circumstances. I could not make it work the way I wanted with what I had on hand.

I was going to use a second relay to let the PCM disable the override switch I added, but quit dicking with it since the cold weather was here. Overheating is just not a concern for me in the winter.

Always interesting to see how other folks solve the problem. I'd love to see some schematics/plans for doing this to compare with my own notes. I'm certain this can be done simply and cheaply with the right pieces and some know-how.

 

[jeeperjohn]

OK, so I guess this confirms that manually grounding the relay throws a CEL if you don't use a diode. I'd be curious to read what the person that used a diode and still got a CEL did exactly. It really seems like it should work just fine. I think I'll try wiring it up loosely and giving it a go. If it works, I'll make it permanent.



I assume here you're talking about wiring in a relay in addition to the OEM relay. This is the route I'll go if I can't get make the OEM relay work the way I want it to. I don't think you need a diode in the OEM fan power wire though. When you manually turn the fan on (and the ECM isn't telling it to be on) the fan motor relay is in the open position so the power wire has no way to back feed that voltage. You do need to fuse the new power wire however.

I was missing that it is a newer jeep. You could use a relay to ground the fan and turn it on if it has a constant hot source. The cel probably comes on when the computer sees current in the fan circuit with no command for the fan to be on. You could wire up a whole separate circuit for the fan with a relay wired in so that when you turn on the fan manually it disables the hot wire in the OEM harness, that way the computer does not see any current in that circuit.

 

[fyrfytr1717]

Gah, big long detailed post, signed me out, post lost...

Hate it when that happens...

Always interesting to see how other folks solve the problem. I'd love to see some schematics/plans for doing this to compare with my own notes. I'm certain this can be done simply and cheaply with the right pieces and some know-how.

Here's what I was thinking, but now that I've drawn it out I can see why it won't work:

With the diode installed as shown, it will prevent PCM from seeing the switched ground (good), but will also prevent the PCM from being able to ground the relay coil (bad). Flip the diode around, and you have exactly the opposite problem.

 

[fyrfytr1717]

With the diode installed as shown, it will prevent PCM from seeing the switched ground (good), but will also prevent the PCM from being able to ground the relay coil (bad). Flip the diode around, and you have exactly the opposite problem.

Sorry, new to diode symbol notation and found out my original reference source was bad. The arrow points in the direction of conventional flow as opposed to electron flow so my above statement is exactly backwards. Still won't work though...

Anyone else have any ideas on how to activate the fan relay without disturbing the PCM? If not, it looks like I'll be tapping a fused power wire into the factory fan motor power wire via an additional relay. I was really hoping to avoid running a separate power wire, but it appears to be unavoidable.

 

[gradon]

That is the conclusion I have come to. I still dig how easy it was to grab a rear wiper switch from the jy, put it in the blank switch panel, connect it to ground and the db/pk wire at the relay, and activate the fan whenever I want.

 

[fyrfytr1717]

That is the conclusion I have come to. I still dig how easy it was to grab a rear wiper switch from the jy, put it in the blank switch panel, connect it to ground and the db/pk wire at the relay, and activate the fan whenever I want.

You're still getting the CEL that you mentioned in your earlier post, right?

 

[jeeperjohn]

You could always use a relay to kill power to the CEL

 

[MrJCRod]

I have a 2001 and I have successfully wired the cooling fan to be controlled by an override switch or by the computer with temp and a/c and I also wired in a master kill switch to prevent it from coming on when in deeper water holes. No CEL either... It all works off the ground from the pcm to the relay. if you cut into that wire and take the pcm signal to another relay before the fan relay and have that new relay send the ground signal to the fan relay it will fool the pcm into thinking everything is normal (no CEL). The ground from the new relay will trigger the fan relay with temp and a/c. On that ground wire you can wire in a switch to send that wire ground to manually turn the fan on and also a master kill switch to prevent it from coming on in deeper water holes... sounds long winded but it took me a long time to think it up and it works perfectly.... basic idea is to put in another relay to trick the computer into thinking it's the fan relay but really it will just send a ground to the fan relay when it is triggered by the pcm... I will work on drawing up a diagram... No diodes... pcm is isolated with new relay...

 

[fyrfytr1717]

I have a 2001 and I have successfully wired the cooling fan to be controlled by an override switch or by the computer with temp and a/c and I also wired in a master kill switch to prevent it from coming on when in deeper water holes. No CEL either... It all works off the ground from the pcm to the relay. if you cut into that wire and take the pcm signal to another relay before the fan relay and have that new relay send the ground signal to the fan relay it will fool the pcm into thinking everything is normal (no CEL). The ground from the new relay will trigger the fan relay with temp and a/c. On that ground wire you can wire in a switch to send that wire ground to manually turn the fan on and also a master kill switch to prevent it from coming on in deeper water holes... sounds long winded but it took me a long time to think it up and it works perfectly.... basic idea is to put in another relay to trick the computer into thinking it's the fan relay but really it will just send a ground to the fan relay when it is triggered by the pcm... I will work on drawing up a diagram... No diodes... pcm is isolated with new relay...

I was thinking this could be done with a second relay, but couldn't wrap my head around how to go about doing it. Thought maybe the second relay idea was overthinking the problem. I'll try to make up a diagram following your description, but if you could sketch it out I'd appreciate it as well. Thanks!

 

[fyrfytr1717]

OK, so here's my sketch of what I think you were thinking. Please let me know if this is the same way you wired it...

Just to keep it simple, I drew it up with only a forced "on" position using an ON/OFF switch. Looks like it should work perfectly:

1. PCM off and switch off - new wiring is invisible to the PCM
2. PCM on and switch off - PCM activates new relay which in turn activates fan relay / PCM isolated by new relay
3. PCM off and switch on - switch activates fan relay / PCM isolated by new relay
4. PCM on and switch on - fan relay activated by both new relay and switch / PCM isolated by new relay

To allow for a forced "off" position, you would simply use an ON/OFF/ON switch. One ON input would be connected to ground as shown in the diagram, the other ON input would be connected to the load side of the new relay, and the switch output would go to the coil side of the fan relay.

The only thing I'm not liking about this is that I've already wired up my Fan Override switch in my overhead console, and it is wired to switch 12V+. This means I either have to wire in a second new relay (12V+ activated, grounded on the load side) in place of the switch in the above diagram, or I need to take down my OHC and rewire the switch to send a ground signal instead...

 

[MrJCRod]

OK, so here's my sketch of what I think you were thinking. Please let me know if this is the same way you wired it...

Just to keep it simple, I drew it up with only a forced "on" position using an ON/OFF switch. Looks like it should work perfectly:

1. PCM off and switch off - new wiring is invisible to the PCM
2. PCM on and switch off - PCM activates new relay which in turn activates fan relay / PCM isolated by new relay
3. PCM off and switch on - switch activates fan relay / PCM isolated by new relay
4. PCM on and switch on - fan relay activated by both new relay and switch / PCM isolated by new relay

To allow for a forced "off" position, you would simply use an ON/OFF/ON switch. One ON input would be connected to ground as shown in the diagram, the other ON input would be connected to the load side of the new relay, and the switch output would go to the coil side of the fan relay.

The only thing I'm not liking about this is that I've already wired up my Fan Override switch in my overhead console, and it is wired to switch 12V+. This means I either have to wire in a second new relay (12V+ activated, grounded on the load side) in place of the switch in the above diagram, or I need to take down my OHC and rewire the switch to send a ground signal instead...

That is how I have it (wiring diagram). I also wired an interrupter switch on the ground wire (DB/Pink to original fan relay) to allow me to completely shut off the fan so when I have the Jeep in deep water I can make sure it wouldn't come on. I would think the electric motor may come into a lot of resistance when submerged and possibly cause a fuse to blow so my master off switch will prevent that... Otherwise, I completely got rid of my heat soak problems (cyl 3 misfires). Between this mod and the home made hood vents I did, I haven't had the rough idle on restart that used to bother the heck out of me...

 

[MrJCRod]

The only thing I'm not liking about this is that I've already wired up my Fan Override switch in my overhead console, and it is wired to switch 12V+. This means I either have to wire in a second new relay (12V+ activated, grounded on the load side) in place of the switch in the above diagram, or I need to take down my OHC and rewire the switch to send a ground signal instead...

What type of switch did you use? If it's one that lights up then leave it alone and run a second relay. I didn't mess with mine too much but I may add another relay because when I wired up my switch to send a ground signal the light on the switch stayed on all the time. Sending 12v+ would let my light on the switch work the way it should but with the ground it doesn't so right now my light is not hooked up on the switch.

 

[fyrfytr1717]

What type of switch did you use? If it's one that lights up then leave it alone and run a second relay. I didn't mess with mine too much but I may add another relay because when I wired up my switch to send a ground signal the light on the switch stayed on all the time. Sending 12v+ would let my light on the switch work the way it should but with the ground it doesn't so right now my light is not hooked up on the switch.

Yeah, that's exactly my problem. It's a Carling switch that lights up when in the on position. I was going to look at the internal wiring schematic for the switch today and see if I could make it work the other way around. If I recall though, the switched circuit and the indicator lamp share a common connection somewhere inside the switch.