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  #1  
Old August 6th, 2013, 13:35
1990Pioneer 1990Pioneer is offline
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Exclamation Cooling fan diode???

Hello all, it has been 7 months since my last confession**Seriously though, I had modded the XJ, worked out the bugs and she's been one of the most reliable vehicles I have ever owned. My question is this, what is the purpose of the orange diode that sits on the driver side behind the head light near the fender wall? The engine runs great, I just happened to notice that the auxiliary fan hasn't ran yet this summer! I ran power from the battery to check its operation, it runs great. The temperature switch that screws into the radiator is open line all the time, even after driving for 30 minutes in 90 weather. I just installed the switch befroe summer, it could be bad. I'm wondering what role the diode plays in all this? I removed the diode and connected the 3 wires directly to each other and the auxillary fans runs whenever the ignition is turned on, engine running or not. AC running or not. I already have a toggle switch ran to that corner but I personally prefer to let the switches and relays do their job, If anyone out there can tel me the ins and out on this diode I would appreciate it.
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  #2  
Old August 6th, 2013, 15:19
bigdaddyjlove bigdaddyjlove is offline
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Re: Cooling fan diode???

I am not aware of a "Diode" in the cooling fan circuit. There is a ballast resistor on the drivers fender in Renix Jeeps, but it doesn't affect the cooling fan.

If the fan works when you apply power, check the relay and the switch.
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  #3  
Old August 6th, 2013, 20:58
SuperRA SuperRA is offline
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Re: Cooling fan diode???

Well, taking a quick look at the engine cooling wiring diagram, the circuit that energizes the AC clutch also energizes the cooling fan relay. (So the cooling fan always turns on when AC is turned on) The diode is there to prevent the ac clutch from energizing when the temperature switch energizes the cooling fan relay.

It's much clearer if you see the wiring diagram, but I can't share it.

Connecting all three wires will connect your temp switch to the AC clutch to the fan relay coil. So if your temp switch is always open, your fan relay is getting a feed from the AC clutch circuit. If this is true, your AC clutch should be energized whenever the fan is running. Verify if this is happening or not. It still doesn't explain why it is energizing when the ignition is turned on regardless of the AC on or off.

Also, the wiring diagram I'm looking at is for an 87. I'm assuming a 1990 (if that's what you have according to your username...you never mentioned your year and other info) is the same.
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  #4  
Old August 7th, 2013, 04:25
1990Pioneer 1990Pioneer is offline
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Exclamation Re: Cooling fan diode???

(1990 Cherokee Pioneer XJ) Thank you for chiming in! Last night I wired the diode back in. I should have DC voltage running to the radiator temperature switch all the time correct?? At least on one wire, so when the switch closes the aux fan comes on right? I don't have DC volts to the switch on either wire. When I turn on the AC, the aux fan runs just fine. I noticed the temp switch never did close ?? So,if that's bad ,that's one thing. But shouldn't I have voltage to the temp switch?? The cooling relay is the only black relay that is on the firewall, drivers side correct? I can feel the coil energizing in it when I plug it in. I feel like the issue is probably something very simple. I hope im not over thinking this one??? Any help on this would be greatly appreciated!
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  #5  
Old August 7th, 2013, 04:30
1990Pioneer 1990Pioneer is offline
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Re: Cooling fan diode???

I also wired in a toggle switch to the cab for now so I can run the aux fan if needed. Not my favorite way of doing it but it will work until I get this fixed.
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  #6  
Old August 7th, 2013, 06:51
bigdaddyjlove bigdaddyjlove is offline
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Re: Cooling fan diode???

Quote:
Originally Posted by SuperRA View Post
Well, taking a quick look at the engine cooling wiring diagram, the circuit that energizes the AC clutch also energizes the cooling fan relay. (So the cooling fan always turns on when AC is turned on) The diode is there to prevent the ac clutch from energizing when the temperature switch energizes the cooling fan relay.

It's much clearer if you see the wiring diagram, but I can't share it.

Connecting all three wires will connect your temp switch to the AC clutch to the fan relay coil. So if your temp switch is always open, your fan relay is getting a feed from the AC clutch circuit. If this is true, your AC clutch should be energized whenever the fan is running. Verify if this is happening or not. It still doesn't explain why it is energizing when the ignition is turned on regardless of the AC on or off.

Also, the wiring diagram I'm looking at is for an 87. I'm assuming a 1990 (if that's what you have according to your username...you never mentioned your year and other info) is the same.

Thanks for the heads up.

I did not know that that was there
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  #7  
Old August 7th, 2013, 10:32
SuperRA SuperRA is offline
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Re: Cooling fan diode???

Quote:
Originally Posted by 1990Pioneer View Post
(1990 Cherokee Pioneer XJ) Thank you for chiming in! Last night I wired the diode back in. I should have DC voltage running to the radiator temperature switch all the time correct?? At least on one wire, so when the switch closes the aux fan comes on right? I don't have DC volts to the switch on either wire. When I turn on the AC, the aux fan runs just fine. I noticed the temp switch never did close ?? So,if that's bad ,that's one thing. But shouldn't I have voltage to the temp switch?? The cooling relay is the only black relay that is on the firewall, drivers side correct? I can feel the coil energizing in it when I plug it in. I feel like the issue is probably something very simple. I hope im not over thinking this one??? Any help on this would be greatly appreciated!
NO, the voltage to the radiator temp switch is only present in the "run" and "start" positions. The permanent voltage to the fan is to the relay (driver's side fender). So you should have DC volts to one wire of the radiator switch when the key is turned to "run". If you don't have that, then you have a problem possibly with the wiring. How did you check the temp switch? I would check for continuity with a meter when the correct temp is reached. (190F according to the wiring diagram)

So when you say "plug in" the relay, you plug it in from it already being removed? And when you do you feel it energizing? If it truly does energize, then your fan should turn on. (which we know works since it comes on with the AC)

Yep usually problems are simple, but you just have to find em. Hopefully you'll figure this one out.
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  #8  
Old August 7th, 2013, 18:52
1990Pioneer 1990Pioneer is offline
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Re: Cooling fan diode???

I checked the switch for resistance with my meter. Open line even after 30 minutes of driving in 90 degree weather. I unplugged the relay while the key was in the "run" position and I could hear and feel the contacts closing as I plugged it back in. I do have good DC voltage at the relay. I also have it on the two orange wires that are attached to the white porcelain mount with two male spade connectors on it that mounts to the drivers side firewall.
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  #9  
Old August 7th, 2013, 23:58
SuperRA SuperRA is offline
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Re: Cooling fan diode???

Quote:
Originally Posted by 1990Pioneer View Post
I checked the switch for resistance with my meter. Open line even after 30 minutes of driving in 90 degree weather. I unplugged the relay while the key was in the "run" position and I could hear and feel the contacts closing as I plugged it back in. I do have good DC voltage at the relay. I also have it on the two orange wires that are attached to the white porcelain mount with two male spade connectors on it that mounts to the drivers side firewall.
Well, 30min of driving in 90 degree weather doesn't necessarily mean that the engine coolant reached 190F. Your mechanical fan could have been doing the job.. Try to get an infrared thermometer to check the temperature of the radiator.

I believe the "porcelain mount" is the fuel pump ballast resistor which I believe would have nothing to do with this problem.

What I'm asking about your relay is that when you feel it energizing, does the fan turn on. Because anytime that relay is energized, the fan should turn on regardless of the key ignition position.
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  #10  
Old August 8th, 2013, 04:02
1990Pioneer 1990Pioneer is offline
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Re: Cooling fan diode???

No, it doesn't turn on when the relay is energized. It shouldn't though, The AC is off, The temp switch is open line etc...I need to check the relay. I actualy swapped the relay with another one and it does the same thing.
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  #11  
Old August 8th, 2013, 11:44
SuperRA SuperRA is offline
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Re: Cooling fan diode???

Then that's weird because that would indicate that your fan (or fan's circuit) is not working, but as you've said before, the fan comes on with the AC... Either that or the relay isn't really energizing upon plugging in (which it shouldn't normally unless the AC is on or the rad temp is at 190F) I dunno, it really is weird.
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  #12  
Old September 16th, 2018, 13:28
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Ecomike Ecomike is offline
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Re: Cooling fan diode???

I am doing some reading DD on this "diode" topic. I have 3 renix rigs that I bypassed the Temp-switch in the radiator on, so they run when ever the ign-switch is on. I have stock AC, never saw a diode, never seen the E-Rad-fan cycle ever in 15 years. But I think I have seen either a diode or bleed resistor on the AC clutch + feed.

Anyone know any more about this topic? I have run into some interesting chat on Facebook about it, But this is the first I ever heard of a diode on the E-Rad-fan/ Temp-switch stuff???

Quote:
Originally Posted by SuperRA View Post
Well, taking a quick look at the engine cooling wiring diagram, the circuit that energizes the AC clutch also energizes the cooling fan relay. (So the cooling fan always turns on when AC is turned on) The diode is there to prevent the ac clutch from energizing when the temperature switch energizes the cooling fan relay.

It's much clearer if you see the wiring diagram, but I can't share it.

Connecting all three wires will connect your temp switch to the AC clutch to the fan relay coil. So if your temp switch is always open, your fan relay is getting a feed from the AC clutch circuit. If this is true, your AC clutch should be energized whenever the fan is running. Verify if this is happening or not. It still doesn't explain why it is energizing when the ignition is turned on regardless of the AC on or off.

Also, the wiring diagram I'm looking at is for an 87. I'm assuming a 1990 (if that's what you have according to your username...you never mentioned your year and other info) is the same.
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34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091
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  #13  
Old July 30th, 2020, 04:04
tempest411 tempest411 is offline
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Re: Cooling fan diode???

I've heard of it! Mine melted down on me last night. Now I've got several feet of wire to repair, and a couple diodes to tie in.
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Old July 30th, 2020, 06:10
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Ecomike Ecomike is offline
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Re: Cooling fan diode???

Quote:
Originally Posted by tempest411 View Post
I've heard of it! Mine melted down on me last night. Now I've got several feet of wire to repair, and a couple diodes to tie in.
I'd be curious to know where in the wiring the diode is/was that you speak of and the part number.

I have though of replacing the one on my AC clutch, to if a new one lets more peak voltage/amps get to the AC clutch on mine
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34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091
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  #15  
Old Yesterday, 04:20
tempest411 tempest411 is offline
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Re: Cooling fan diode???

Quote:
Originally Posted by Ecomike View Post
I'd be curious to know where in the wiring the diode is/was that you speak of and the part number.

I have though of replacing the one on my AC clutch, to if a new one lets more peak voltage/amps get to the AC clutch on mine
The radiator fan diode is at the front DS corner of the engine bay. It's this little orange thing with three wires coming out of it. This is not the diode on the AC compressor for flyback voltage spike protection. Eliminating that particular diode would only result in damaging other electronic components in your Jeep, and won't increase the current reaching the clutch at all...Unless the diode is bad, but then you'd have a short circuit and fried wiring.
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