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Electrical peeps - wiring rad fans into link this weekend. relay question

EfiniX

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I'm using a standard SPDT relay. This would normally be straightforward, but I've heard mention that the ECU switches using ground. So normally, if I wanted something to come on with an SPDT relay, I'd wire pin 30 to 12v, pin 87 to the thing I'm powering, ground pin 85, and put my voltage switch on pin 86. Pin 87a would go unused.

I'll, of course, use link to activate the EGR-S pin (53) and put a multimeter on it to see what it does. But as a matter of saving time, is there something I should know if I'm used to switching with voltage?
 

CutlassJim

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Are you talking about a cheapo relay like this?

Relay_0332209137_Drawing.gif


86 to positive and 85 to the ECU. the wiring on the other side doesn't matter at all. You could even be like those crazy 80's Japs and interrupt the ground on whatever your are powering! /ubbthreads/images/graemlins/jawdrop.gif
 

GSTwithPSI

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Is there a reason you want to use a separate relay? The easiest way to do it would be to tap into the ground wire for the high speed fan relay, and run a wire from there to whatever ECU output you want to use. At that point, you'll basically be using ECMlink to control the factory high speed fan relay. This relay is normally controlled by the fan switch on the bottom of the radiator.

I'm not sure exactly how you intended to wire the circuit, but if you do it like outlined above, you'll still have redundancy in the circuit. The fan switch will still be able to operate the cooling fan independent of ECMlink. Mark has outlined this procedure in a few threads now I think. Edit: Here's the other thread: click

You'll tap the LB wire that runs from the "radiator fan motor relay (HI)" to the "engine coolant temperature switch". You can easily locate this wire either at the fuse box where the relay is on pin 2, or at the fan switch itself at the bottom of the radiator.
img.php
 
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EfiniX

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Cutlass: yup, that's the relay. In fact, it's already in there from when I did my radiator swap and had two slim fans installed.

GST: Well, that's an excellent question. The car came to me with the fan wiring already hacked-up. Right now, the fans come on at 140F and after searching more than once with Evan, we can't, for the life of us, figure out what the PO did to achieve that bit of voodoo. The temp sensor is stock and there don't appear to be any resistors soldered in anywhere.

So the reason for the relay question is because there's a relay already from when I had the new radiator installed. For me, it's just a matter of pulling a wire from pin 53 and sticking it on the correct terminal.
 
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CutlassJim

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If it wasn't already messed with I would totally go with GSTwithPSI's setup with the redundancy. You want your fan turn on temp to be slightly (~10*) above your thermostat setting for everything to work like it's supposed to. I have mine set up to turn on at 190 and off at 170 with a 180 thermostat.
 

EfiniX

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I had a minute to put a multimeter on the car this morning and I figured out how the fans are wired up.

I've got two single-speed slim fans on my radiator. On is pulling, the other is pushing. The fans are identical, with flow being determined by voltage polarity. The relay runs the fan that is pushing, confirmed by the operation of the puller fan with the relay pulled out.

With the car off and the relay pulled, I see 12v on pins 30, 86, and 85. So I'm guessing that the radiator thermostat is basically a thermo-switch, providing 12v until it hits a certain temp, at which point it grounds the pin. When this happens, the puller fan circuit closes and the fan kicks on. Additionally, pin 85 now has ground, which clicks the relay and turns the pusher fan on.

I'm guessing to get this wired into link, I just need to disconnect the radiator thermostat from the relay and connect the EGR solenoid pin from the ECU harness. Then, at the threshold I set, the ECU will ground pin 85 and my fans will come on.

Do I have this right? I figure the big no-no here is feeding 12v back into the ECU...
 

GSTwithPSI

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No, absolutely do not connect relay pin 85 to the ECU output. The ECU driver is only designed to ground side switch a very low amp circuit. In the circuit you've drawn, if you connect the ECU to relay pin 85, the fan motor will go to ground through the ECU, which would be bad.

I don't even know how your circuit functions. As you've drawn it, the puller fan goes directly to ground through the fan switch. The fan switch is meant to function much like the ECU, in the sense that it's intended to control a low amp circuit's path to ground. That low amp circuit should be the coil for the high speed fan relay (or any relay). In your circuit, it's controlling the fan motor's path to ground, and I'm surprised it's even working given the amperage a typical fan motor draws.

Lastly, you have a positive wire drawn going to the fan switch. The fan switch is just a ground interruption that's switched on or off according to temperature. There should not be any power going to the fan switch.

My advise would be to rip all that sh*t out and start over. The circuit you currently have is overly complex, and isn't even configured correctly. Wire your fan motors back in like stock, and run a single wire to the high speed fan relay's ground wire to your ECU output. Then, reverse the polarity on whatever fan you want to run in reverse. Done. It might be more work to unfuck the mess you have, but it's better than trying to make what you currently have work properly.

If you want, I can draw the circuit up for you if you need help.
 

EfiniX

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I didn't touch a thing yesterday as I couldn't noodle out where the low voltage should be coming from. IIRC, I did see ~0.6v of the fan switch (what I've been calling a thermoswitch) when it hit 140. It's that my low voltage source? If so, this all becomes very easy.

Also, the skin fans aren't dual-speed. They just come on and run.

Thanks for the feedback. I'm guessing two things are going on, here. First, I probably screwed up my diagram since I did it from memory. Second, I think the fans were wired in a way that if I chose to use link for control, I could hook it to the relay and basically have one fan that clicked on at 140°, and they other controlled by link.

Basically if I know where to pull my low voltage from, I'm set. LV into pin 86, link to 85, and the fans 12v across 30/87.
 

GSTwithPSI

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I'm not sure where your probes were when you were testing. If they were placed on each side of the fan switch, you're just reading the voltage drop across the switch, or whatever two points were between you meter leads.

According to your circuit, both fans rely on the fan switch at the bottom of the radiator to come on. That means only the fan switch can be responsible for making the fans come on at the wrong temp (140*). If your fans are coming on at the wrong temp, it's because of the fan switch...That's assuming the diagram you drew was accurate.

I'm not sure what you mean by where to pull low voltage from. Pin 86 should go to 12v +. Pin 85 should go to the fan switch, and your ECMlink output ONLY. Meaning, if you have a fan grounded to that pin (85), remove it unless you want to cook your ECU. I'd remove it anyway, since the fan switch was never intended to act as a relay. Wire fans across 30/87 like you said, with the polarity of the pusher fan swapped.
 

EfiniX

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When probing, I was grounded to the battery, so wherever I saw 12v, 12v was there. it was really odd to see 12v on both sides of the relay coil until the fan switch clicked on, but in retrospect, since the fan switch is actually switching to ground, I suppose it's not that weird after all.

And yes, 100% the fan switch (or at least something in the fan switch circuit) is causing the fans to come on at the wrong temp.

And forgive my electrical terminology. I'm an engineer, just not an electrical engineer. I do, however, greatly appreciate how things are complicated when someone is using the wrong terms.

My question regarding where "low voltage gets pulled from" is expressed better with a longer question actually typed on a computer and not a phone. This is all about the relay and the ECU and how I understand the circuit to work.

The fans are easy. All they want are 12v and ground and they are good to go. They will get constant power on the appropriate-to-turn-in-the-right-direction polarity, and i'll ground them through the SPDT relay I have (pins 30/87). It's the relay coil and the ECU control that's the rub.

As you've said, the ECU is a ground switch. I understand this to mean that when switching a relay with the ECU, you have a low-voltage source on one side of the coil (86) and a ground source on the other side of the coil (85). When the ECU clicks the relay "on", it is essentially completing the circuit by allowing the coil to ground through the input pin (on the ECU). If this understanding is incorrect, then of course me wondering where that low-voltage source on pin 86 comes from is also incorrect.

How you describe it, I hook pin 86 directly to the battery. Pin 85 goes to the fan switch and the ECU? With this setup, won't the fans just turn on early when the fan switch grounds? How does the ECU provide control at this point? A bit more freaky is how the ECU doesn't get burned up by sitting on a 12v circuit off the battery. (this is why I'm thinking my understanding of how the ECU is "switching" is not correct). Frankly, I'm happy to take the fan switch out of the equation if that's an option, but maybe it's not.

I see the Redskins start in an hour, so thanks for taking time from a morning that may soon be dominated by football...
 
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GSTwithPSI

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Fundamentally, all circuits work the same. For simplicity sake, all you need is power, ground, and a load.

The load is your fan.

Your fan needs power, and ground.

To power the fan, provide a direct path to full battery voltage. This should probably consist of a single wire running from the fan motor to 12v +.

To ground the fan, you'll use a relay. You'll control that relay by both the fan switch, and ECMlink. Anytime the relay is activated by either the fan switch or ECMlink, your fan gets a direct path to ground (through the relay) and the fan runs full speed.

By using both the fan switch and ECMlink, you'll create redundancy in the circuit. The fan switch should activate your high speed fan relay at around 206*. The main reason you'd want ECMlink fan control is to activate the fan at a temp under 206*. So, you'll basically have two paths to ground. One through the fan switch at 206*, and another through ECMlink at whatever temp you specify. These two grounds will work independent of one another, and will both provide the high speed fan relay coil with a path to ground, which in turn activates the relay coil and gives the fan itself a path to ground. There should be little to no voltage on the ground side of this circuit, since it should be consumed by the relay coil.

You shouldn't have to worry about back feeding the ECU voltage unless your circuit is all screwed up (which is sounds like it might be). That's why I suggested putting everything back to stock, and going from there. I can't account for any variables that have been introduced by POs dicking with the circuit and/or wiring harness. Everything I'm saying relies on modifying a properly working stock fan circuit.
 
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MuffinMan7580

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The fan switch at the bottom of the radiator controls low speed (green and blue wires) and the blue and black wire at the back of the thermostat housing controls high speed.
 

EfiniX

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portland, or
So I can use the 12v bat power for one side of the relay coil, and the ECU for the ground on the other side? I'm assuming my fan switch is fucked and I'll ultimately be using Link for 100% of the fan control.

Edit

I suppose running the coil of 12v must be ok since without a transformer, 12v is 12v. It's about amperage and so long as the ECU isn't part of the fan motor circuit, it's ok...

Right?
 
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GSTwithPSI

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Quoting MuffinMan7580:
The fan switch at the bottom of the radiator controls low speed (green and blue wires) and the blue and black wire at the back of the thermostat housing controls high speed.



^Yeah. I shouldn't say "fan switch".

Per the diagram:

Engine coolant temperature switch = located on the back side of the T-stat housing
Thermo sensor = located on bottom of radiator

img.php


You can use either one to activate your fan, since basically just need to hijack the relay operation via ECMlink. That was the point I was trying to make.
 
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MuffinMan7580

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Quoting MuffinMan7580:
The fan switch at the bottom of the radiator controls low speed (green and blue wires) and the blue and black wire at the back of the thermostat housing controls high speed.



Fan switch should be green and black wires, not sure why I put blue.
 
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