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Manual Switching of the auxiliary fan

gradon

gradon

NAXJA Forum User
Location
DC
All right boys and boys, I finally wired a switch to control the stock auxiliary electric fan. The way the fan turns on normally, the pcm provides a ground for the aux fan relay, which then provides voltage to the fan. The pcm engages the ground when the temp hits 217*(according to my 96 fsm) or when the a/c compressor is engaged(a/c or defrost mode). Basically you have a switch with input side grounded and the output side will go to the aux fan relay @ the pdc on pass side fender. On my 96, the aux fan relay ground wire is Dark Blue w/ Pink stripe(DB/P). I removed the PDC to get access to the wiring underneath the relays. Now with the switch on, the fan will be on continuously until you turn of the ignition. With the switch off, the fan will turn on when it normally does. It uses existing fuse and relay.
P1120048.jpg

P1120050.jpg
P1120051.jpg
P1120052.jpg

Now on my brother's 95 dual e-fan setup, he used a second relay for the second fan and had it engaged by the 12v output of the first relay(his doesn't get too hot so if it ever hits 217 or the ac is on, both fans will engage simultaneously. Here's some of his pics:
PermaCool_24.jpg
PermaCool_26.jpg
PermaCool_30.jpg
 
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I did this quite awhile ago on my 91 OBD1 MJ. I used a new SPST dash switch (an XJ rear defroster switch) to apply a ground to ECU pin 31, the existing ECU ground output that turns on the aux fan. This applies to 91-95 OBD1 XJs and MJs. When the dash manual control switch is open, the ECU controls the aux fan normally. I run two electric fans and wanted the ability to control the aux fan manually if needed. Here's the wiring diagram:

FanSwitch.jpg
 
Exactly--I tapped into it by the 5 on the relay. I like using factory switches for whatever I need(good JY item). I'm currently using three of the four available locations(my bonestock XJ had blanks).
 
Well I have to let yall know that I have a 1491 Radiator fan control circuit problem CEL due to my mod. I don't know if the obd1s will be more forgiving. Anyhow, it works like a charm and I'll deal w/ it and check the cels every now and then to make sure there aren't new ones.
 
No problems or codes on my OBD1. Does turning on the manual control switch trigger your CEL or has it been there all the time? Can you clear it, and if so, does it come back immediately?
 
sp5368 said:
Thank you for the pictures but it does not apply to my application he is using a hot to turn on the fans. The wire I am looking for is a ground control for the relay which allows the fan to turn on this relay is activated by a ground connection.
Click to expand...

No one is using a hot lead to trip the aux fan relay above, both use a ground signal from the switch.
 
gradon said:
Well I have to let yall know that I have a 1491 Radiator fan control circuit problem CEL due to my mod. I don't know if the obd1s will be more forgiving. Anyhow, it works like a charm and I'll deal w/ it and check the cels every now and then to make sure there aren't new ones.
Click to expand...
It might be that if you put a diode on the CPU stub and keep ground signal from returning to the CPU from your switch the CEL won't fire
 
Yes, the moment I switch the fan on, I'll get that 1491. I've thought about the diode and will give that a shot and report back.
 
gradon said:
Yes, the moment I switch the fan on, I'll get that 1491. I've thought about the diode and will give that a shot and report back.
Click to expand...

Yeah, I think that's in order. I'd place the diode in the circuit between the PDU and the switch splice with the cathode banded end of the diode pointing to the aux fan relay to prevent any signal backfeeding into the PDU. It should prevent the code fault.
 
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I could not get the diode set up to work. The PCM senses both ways, it looks for the command of the relay, so I just ended up installing a relay by the pass side tying into the fan feed wire in the main loom. It only took an hour start to finish. Works great.
 
Hallo. If you do have an older JEEP, keep it simple, Use a relay extra and a ground switch in the cabin .No problems with the ECU and no use of dodes.:dunce:

click on pic for bigger pic.

'92 XJ
 
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Don't have time for a drawing, but: I found the fan + wire in the main loom, cut open and soldered a spliced into the fan wire, use 10-12 ga for this, run the same ga wire from your fuse box, I used a fusible link that was installed on the lug that you battery feed cable is mounted on the side of the fuse block, you could also install a 30 amp fuse in a good blade style fuse holder. mount a switch in your dash, I tied into the cig lighter feed, its controlled by the Ign switch so it will only be hot with your key on. run this wire out to where you are going to mount the relay, there is a good spot right next to the hood hinge, out of the way and you can put all of there wires into the factory wiring convolute, making for a neat install. You will also need a small ground wire which you can just run a tex screw hidden behind the main loom. User a 30/40 amp Bosch relay.
I believe from memory that the relay is wired like this: term 30 to fan feed, 87 to positive, 85 and 86 are the switch and ground.
 
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