I installed E-fans on my 2001

[ScottyBoy]

This is a step by step tutorial on how to upgrade any 00-02 Tahoe, Yukon, or Suburban to the 05-06 GMT800 electric cooling fans. This same setup can be used on 03-04 trucks as well, however the only difference is the wiring that connects to the PCM. I will also add that a custom tune from someone like Blackbear Performance (http://www.blackbearperformance.com/)(who is a site sponsor by the way) is also needed, because the pins to control the fans in the PCM need to be turned on with the tuning software.

First of all, you need to measure your radiator to see what size it is. Some trucks came with a smaller radiator, (28 inches wide I think) and some have the larger radiator, which is 34 inches wide. The 05-06 Tahoe/Silverado electric fans can only be used if you have the larger radiator. So if you have the smaller one, you need to upgrade your radiator first. If you have the 34 inch radiator, like I do, the fans will bolt right up as if they were made for your truck. The holes for the fan to bolt on are already in the radiator support. It uses the same bolts as the radiator. So if you didn't get the bolts with your new fan, just go grab some radiator bolts off a truck in the junkyard. I got my fans from a 2006 Chevy Silverado in the junkyard. I was also able to pick apart the wiring harness and get that as well. I even got the pin that needs to be added to the PCM harness. So now I have an OEM wiring harness complete with fan relays. This actually clips right onto the side of your underhood fuse panel once you remove the cover. Here is the fans and the harness that I got.
http://i177.photobucket.com/albums/w233/cutdog504/2011-05-23_16-43-45_797.jpg
http://i177.photobucket.com/albums/w233/cutdog504/1021726935_photobucket_42466_.jpg
http://i177.photobucket.com/albums/w233/cutdog504/1021726935_photobucket_42465_.jpg
http://i177.photobucket.com/albums/w233/cutdog504/1021726935_photobucket_42467_.jpg
http://i177.photobucket.com/albums/w233/cutdog504/1021726935_photobucket_42464_.jpg

I cleaned up the harness and added some wire loom to it and made it look cleaner, for a cleaner install.
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03156.jpg
You can buy a pre-made harness from Blackbear Performance for a very easy install. Or if you are able to procure the correct pigtails for the fans and the PCM, you can custom make your own harness. Here is a wiring diagram of how the fans are factory wired on the 05-06 GM trucks.
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/efan.jpg
If you have an 03-04 truck, then you will wire it exactly like this diagram shows. But on a 99-02, the PCM only has pin 42 available to use. The other trigger wire has to be connected to the AC compressor clutch relay wire. That wire is positive, so by me using an OEM harness, I had to add a relay to that wire to change it to a negative in order to trigger the fan relay pack, which is set up to be triggered by negative signals from the PCM. This extra relay is not needed if you use the pre-made harness from Blackbear. Thier harness is already setup to use a positive trigger from the AC wire. Now onto the wiring. First you want to remove your underhood fuse panel cover. Not just the lid, the entire cover. You will have to unbolt the corner fender brace in order to get it up and off. Now lift up the fuse junction block to get access to the underside. You will need to splice into the dark green AC clutch relay wire. This is the wire you need.
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03135.jpg
This is where you will tie in your relay (or trigger wire if using a Blackbear harness). The relay needs to be wired as follows:
86-Green AC wire
85-Ground
87-Ground
30-Blue trigger wire on OEM fan relay pack

And here is how your relay should look.
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03132.jpg
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03133.jpg
Now take the green wire on your relay and splice it into the factory Green AC wire with solder and heat shrink tubing.
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03150.jpg
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03151.jpg
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03152.jpg
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03155.jpg
I grounded the ground wire to this bolt on the fender, right below the fuse block.
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03143.jpg

[ScottyBoy]

Now the low speed fan trigger needs to be connected to the PCM. Remove the PCM from its mounting bracket and unplug the wiring harness, which is held in with one screw. Unscrew it and slowly wiggle it side to side until it comes loose. You will need to insert a pin into an empty slot, pin 42 on the side that says "BLUE". Carefully remove the blue plastic cap on the side of the harness that plugs into the PCM. (Sorry, I didn't get a picture of that)
Here is where you need to insert your green trigger wire pin.
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03126.jpg
The empty spot labeled 42. I poked an awl thru the yellow rubber to make it easier to get the pin thru.
Here is the inner side with the blue cover removed.
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03127.jpg
Now take your pin, and carefully push it thru the pin 42 hole until it is fully seated just like the rest of the pins.
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03128.jpg
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03129.jpg
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03130.jpg
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03131.jpg

Now you need to mount your relays. If you are using a Blackbear harness, you can mount them wherever you choose. But I have the OEM harness, so I am putting it right alongside the fuse block, right where it sits on a 05-06 truck.
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03136.jpg
It just clips right in.
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03138.jpg
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03139.jpg

And then the main power feed for the relay needs to be connected to the battery, and the ground needs to be secured to a factory boly on the frame or body. I secured mine to the horn mounting bracket, because the OEM harness grounds in that general area on a 06 truck.

I just zip tied my harness alongside another factory wire loom that runs alongside the bottom of the radiator.

Now that the wiring is squared away, on to the actual fan swap. First, you need to remove your air intake tube. Next, you want to remove the upper half of your fan shroud, which is held on with two 10mm bolts on the top, and two plastic push rivets on each side. Notice the empty bolt hole just to the left of the 10mm bolt that secures the fan shroud. This is where the electric fan shroud will bolt up to.
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03159.jpg
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03161.jpg
I find that using a door panel removal tool is perfect for getting the plastic rivets out. If you dont have one, a pair of wire cutters will work too.
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03162.jpg
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03166.jpg

Now once the yop half of the fan shroud is off, you need to remove the factory fan by unbolting the fan clutch. You need a big ass wrench and a hammer. Hit it with the hammer to turn it counter clockwise to break it loose. I used a pair of vise grips on mine. I have heard of some people also using an air chisel to get it off as well.
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03167.jpg
Now once you get the fan off, the bottom half of the fan shroud will simply lift right out.
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03168.jpg
Now just drop your new electric fans down where the fan shroud was. You will have to do a little wiggling to get it around the radiator hoses. The bottom of the shroud rests on the radiator support just like the original fan shroud did. It also rests in the "hooks" that are molded into the radiator tank.
Now look at the top and the two monting holes should line up perfectly with the two holes in the radiator support. Now just bolt it in.
Then I climbed underneath and finished securing all the wiring.
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03177.jpg

Now just bolt your air intake tube back on and you are done!
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03179.jpg
http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03181.jpg


http://i177.photobucket.com/albums/w233/cutdog504/Truck%20mods%20and%20repairs/DSC03176.jpg

And one more thing, if your truck has the 105 amp alternator, I strongly suggest that you upgrade to the 130 amp or 145 amp version. I have the 130 amp one in mine, and I am noticing my volts guage drop from 14 down to 12 or 13 when both fans are on and I am idling. The volts will increase if I rev the engine though. I am planning on upgrading my alternator when I get more funds.

[yukondoit]

Nice write up! :Handshake: This is getting added to my to do list.

[puckhead]

Very nice write up! Thanks!

[waxworkz]

i did the same thing but tapped my ac wire off the wire bundle that comes down close to the alt. i also used a BB harness. took all of 30 mins

[gpracer1]

Couple of questions.....
For OEM harness,
Instead of using the positive wire from the AC clutch, why dont you use the negative trigger from the PCM to the AC clutch relay for high fan?

What happens when you go faster than the fan cut off speed in the tune when the AC is on? Do the fans stay on high? Do both fans stay on high?
NOPE.

I have a 99 with 05 fans and oem harness, and 0411 swap.
I have the PCM control the low speed fans, and the AC clutch relay trigger negative hooked to the high speed fans trigger wires.

Now between the PCM AC clutch trigger wire and the AC clutch relay, I broke the connection with an extra relay. This relay is commanded closed (so the high speed will still work when AC on) whenever the low speed fans are on. If the low speed fansturns off due to higher than tune threshold, it interrupts the high speed by cutting the connection from PCM AC request to AC relay.

In other words, at over 45 mph (my tune) All fans turn off even if the AC is on. This way you are not driving on a 600 mile trip at 75 mph with the fans on high because you have the AC on.....pulling 50 extra amps.

[ScottyBoy]

I emailed Justin @ Blackbear several times before I did the wiring. He said tying into the negative AC trigger wire was a bad idea (he didn't go into detail why) and the best way to wire them up was to just add another relay to change the polarity to negative.
Also, the way the fans are wired, both fans are only on high if the PCM low speed trigger is on AND the AC is on. If the PCM trigger isn't active (whether the temp isn't hot enough, or I am driving on the highway) but the AC trigger wire is active, only one fan turns on. The PCM trigger turns both fans on at low speed. The AC trigger turns one fan on at high speed. If both the PCM trigger and AC trigger are on AT THE SAME TIME, then both fans are on at high speed.
So when driving on the highway with the AC on, only one fan is on and I am ok with that.

[gpracer1]

I emailed Justin @ Blackbear several times before I did the wiring. He said tying into the negative AC trigger wire was a bad idea (he didn't go into detail why) and the best way to wire them up was to just add another relay to change the polarity to negative. No idea why that is a bad idea.

Also, the way the fans are wired, both fans are only on high if the PCM low speed trigger is on AND the AC is on. (Mine is the same)

If the PCM trigger isn't active (whether the temp isn't hot enough, or I am driving on the highway) but the AC trigger wire is active, only one fan turns on. Why would you want that since it draws power and cools less than 50mph wind? Also only one fan on is not good, since it will draw air from the fan that is off since it shares the same shroud, which gives you poor cooling airflow.
The PCM trigger turns both fans on at low speed. The AC trigger turns one fan on at high speed. If both the PCM trigger and AC trigger are on AT THE SAME TIME, then both fans are on at high speed.
So when driving on the highway with the AC on, only one fan is on and I am ok with that.
You are ok with one fan on, less cooling and more amp draw while cruising down the road with the AC on?


I made it simple on mine, engine cooling both fans on low.
AC on, both fans on high.
Over a certain speed all fans off.

[ScottyBoy]

Well post up a diagram/schematic and maybe I will rewire mine.

[gpracer1]

Well post up a diagram/schematic and maybe I will rewire mine.

Ill have to do that!

[ScottyBoy]

Yeah, spread the knowledge man. That's why I made this thread, to spread the knowledge with other members. :Handshake:

[Tridaddy]

May I ask what electric fans do for your vehicle?

Why do some vehicles come from the factory with them and others do not?

Thanks

[01Konvict]

He said there from a 06 GMT800 which equals Dorman # 620654 on amazon for $142.05

[Max]

May I ask what electric fans do for your vehicle?

Why do some vehicles come from the factory with them and others do not?

Thanks

Significant improvement in throttle response, fuel economy, and power. Takes parasitic drag off the engine and puts it on the electrical system, which is more than capable of powering the fans especially with an overdrive pulley on the alternator (scoop a bigger alternator if you have a large stereo or at lease a better battery). I netted about 2mpg and 20hp from my efan swap, made a huge difference.

[gpracer1]

Significant improvement in throttle response, fuel economy, and power. Takes parasitic drag off the engine and puts it on the electrical system, which is more than capable of powering the fans especially with an overdrive pulley on the alternator (scoop a bigger alternator if you have a large stereo or at lease a better battery). I netted about 2mpg and 20hp from my efan swap, made a huge difference.

Not to mention faster warm up times, better cooling at idle, better A/C performance at idle or low speed, no roar when taking off when fan locked.
More room to work on engine or access belt, no missing fingers when engine running, less wear on water pump.
Best gains are in hot climates.

[01Konvict]

Doesn't the overdrive alternator pulley wear out the alternator faster? What is a bigger alternator upgrade?

[gpracer1]

Doesn't the overdrive alternator pulley wear out the alternator faster? What is a bigger alternator upgrade?

Actually I think it may help.

Consider that when you are at idle in drive with your foot on the brake.....you are at your lowest engine speed. If you are drawing more than your alternator can put out, your voltage regulator is transitioning from normal operation to "wide open" to try to keep up. I would assume that after a while this would wreak havoc on it. That is of course if you have a big stereo or efans, etc.
The only problem could be if you are constantly at 5500 rpms.

Plus the faster it turns, the more cooling it produces, including idle.

[dwmmatt23]

Question, I already have my dorman fans and am meeting Justin today for my tune. I have a Z71 hoe which has the larger alternator, do I or should I still get the alternator pulley with the BB harness?

[Xav8r]

Similar question for you guys that have done this. I have the 130A alt and am not sure if I need/want the "overdrive alternator pulley" from BBP? Can one of you please explain to me what this is, does, or why I would or wouldn't need it? Also if I do go this route, will this change which size accessory drive belt I will need?

Thanks

[gpracer1]

Similar question for you guys that have done this. I have the 130A alt and am not sure if I need/want the "overdrive alternator pulley" from BBP? Can one of you please explain to me what this is, does, or why I would or wouldn't need it? Also if I do go this route, will this change which size accessory drive belt I will need?

Thanks

A smaller pulley will make the alternator spin faster. This means at idle it will be putting out more power/spinning faster than normal. This way if you have a large draw like fans, your lights wont be dim at night at idle and your gauge wont read 10-11 volts. Yes your belt will need to be slightly shorter.

[Xav8r]

A smaller pulley will make the alternator spin faster. This means at idle it will be putting out more power/spinning faster than normal. This way if you have a large draw like fans, your lights wont be dim at night at idle and your gauge wont read 10-11 volts. Yes your belt will need to be slightly shorter.

Thanks Marc. That's just what I was looking for. How did you go about figuring the proper size belt after your upgrade? Also, I'm not totally familiar with '99's but I note that you have a 140A alt, was that a significant upgrade from stock or was your original similar to my 130A and I need to step up to a 140A? FYI, my truck is not a state of the art AV showroom on wheels!

Thanks again.

[gpracer1]

Thanks Marc. That's just what I was looking for. How did you go about figuring the proper size belt after your upgrade? Also, I'm not totally familiar with '99's but I note that you have a 140A alt, was that a significant upgrade from stock or was your original similar to my 130A and I need to step up to a 140A? FYI, my truck is not a state of the art AV showroom on wheels!

Thanks again.

My original alternator was only 105 amps, and the whole case was different in shape and size than the 140. The belt size was shorter with stock alt and small pulley, but when I went to the bigger alt and put the small pulley on it, I could use the oem belt. :)

[01tahoenjn]

Great thread thanks Scott!!!
How much did this all run you guys!?

[01tahoenjn]

Would these work
http://img.tapatalk.com/45733273-b0a1-81fe.jpg
http://img.tapatalk.com/45733273-b0aa-f8eb.jpg
07+ efans for v8 silverado so it says

[tRidiot]

Ok, I got my 05+ cooling fans and my BlackBear harness. Problem is, it came with zero instructions.

I've got the power and ground wires and the Blue 42 and Green 33 wires.

I currently have a set of generic e-fans hooked up through the rad with zipties (hence I'm now replacing my rad at the same time). They are triggered by a temp probe in the radiator, and also by being tied into the A/C compressor.

I did not get a "tune" from BlackBear... can I make this work without a tune? At least for a little while? It's cold out, so I'm thinking I can get by for a few weeks without fans if I need to (heck, I went most of the summer without them, just had crappy A/C). I'm just wondering if I can hook that A/C wire to the Green 33 wire to get the fans to come on "high" and the Blue 42 wire will trigger them for low?

I'm just a bit confused, as BlackBear's site has zero instructions as to what's needed, just has an option for the tune or the harness, wasn't aware I needed BOTH, if I do. It's not a money thing, I don't mind the $55 for the tune, just that I have to replace my rad sooner than later and was hoping I could either hook things up to run sub-optimally (which ought to be fine in winter) or whatever for the moment.

Someone throw me a bone here?

Never had any communication from BlackBear about my order or shipping, and no instructions, either. Kinda disappointing, I guess.

[Rivieraracing]

Tridiot, check this link out and go to post #34, hook up your main power wire inside the red juction box in the fifth picture and hook your grounds to the bracket bolt that holds the junction box!! http://www.tahoeyukonforum.com/forum/showthread.php?t=9400&page=6

As for rigging up the fans to work on your truck without a tune, I wish I could help you there!! Maybe someone else will chime in on that!!

[ScottyBoy]

No, it will not work without a tune. Not tying into the computer pins anyway. You could hook it up to the temp probe that you currently have, and hook the high speed wire to you AC wire.

[tRidiot]

So green is high-speed? And blue is low-speed? Is that how it works? If so, I COULD potentially hook the blue to my current temperature probe and the green to my A/C compressor. This ought to yield me somewhat normal operation for the short-term.

I just was hoping not to have to put that temp probe back in through the fins on my new radiator. This is already the 2nd replacement I've done...

[tRidiot]

No one?

[Rivieraracing]

Wish I could help you but haven't had to hook my up anyway other than the way it was meant to be hooked up and used!! I'm guessing that the green pin (A/C) is the passenger side fan and the blue pin is the drivers side fan and maybe when it really needs to cool down, the computer will get voltage to both pins which makes both fans kick on!! Just is just a guess though, hopefully someone else will chime in or else PM Jennabear since you have their harness, maybe they can tell you how to rig it up!! Good luck!

[Xav8r]

Hey Guys ... I'm asking for a little help with this one ...

'01 Tahoe, BB tuned, new e-fans and LS1 harness through Justin ...

When I turn on my AC the passenger fan triggers on high, however it cycles from high to OFF 2 to 3 times a minutes. Does this sound normal, or like anyone elses install?

Also, I warmend the truck up and expected the drivers side fan to trigger on HIGH, however never did get it to turn on. Does anyone know what the trigger on temperature setting is for the Blue 42 pin wire? It is cold outside, and I never did get the temp gauge to read above 210, however I did expect to see the fan kick on high after a stable 190+ for 10-15 minutes.

Thanks in advance ...

[Rivieraracing]

Pm'ed you!!

[ScottyBoy]

Jenna told me that the fans dont kick on until 209 degreez.

[Rivieraracing]

That's good to know, I was always curious on when the computer kicked the fans on!! Thanks for sharing the info!

[01Konvict]

I installed mine today and I used M8x1.25 thread bolts for the new fans. The old bolts didn't fit the relocated holes. Just a FYI for reference.

[01tahoenjn]

How are they working!?!

[tRidiot]

Hey Guys ... I'm asking for a little help with this one ...

'01 Tahoe, BB tuned, new e-fans and LS1 harness through Justin ...

When I turn on my AC the passenger fan triggers on high, however it cycles from high to OFF 2 to 3 times a minutes. Does this sound normal, or like anyone elses install?

Also, I warmend the truck up and expected the drivers side fan to trigger on HIGH, however never did get it to turn on. Does anyone know what the trigger on temperature setting is for the Blue 42 pin wire? It is cold outside, and I never did get the temp gauge to read above 210, however I did expect to see the fan kick on high after a stable 190+ for 10-15 minutes.

Thanks in advance ...
Interesting...

Got my BB harness wired in professionally by a local 12V installer who knows well what he's doing. The triggers worked when checked manually against a ground, activated the fans on low and high.

Since I didn't have time to get a BB tune and they said the local event was not looking promising, I had a local guy tune the truck for $75.

I had wired the high-speed trigger to the A/C compressor using a relay to convert it from positive to negative so it would trigger properly. My fans also do what the poster above said, with them cycling on 2-3x per minute with the A/C compressor. I don't really know why my A/C compressor does this, but to my knowledge, it has always done it. Never does my compressor come on and stay on continually, at least not the I've noticed.

The plan was to simply unplug the relay from the compressor to the trigger wire when the tune was complete. However, after the tune, the fans do not work. At least, the computer is not controlling them. The guy showed me on the software where he has the fans enabled by setting them from 2 (no fan) to 0 (2 fans) and various settings, but even with a manual override command from the laptop, the fans will not engage.

So I plugged the relay back in so they would work with the A/C.

Just a frustrating process.

[Xav8r]

A little follow up info from Justin ...

Here are the conditions:

Pin 42 alone, both fans come on low,
A'/C alone, one fan comes on high
Pin 42 and A/C together, both fans come on high

Pin 42 should trigger at around 210 degrees and then back off at 199. And it is very common for the compressor to cycle that much unfortunately.[/SIZE]

I still have not confirmed the drivers side fan is working by either reaching the ~210 temp or grounding out the pin. And I have not seeing the both fans on low, which I'm assuming means I've never reached the temperature threshold.

I am a little bummed to have the AC cycle the passenger fan from high to off so frequently as I can feel the drain on power resulting in increase throttle for the same speed (via either cruise control or foot pressue). Plus it just doesn't seem like the fans or the harness and relay will last long being turned on and off so frequently.

But so far I haven't seen anybody post that they've uninstalled the efans or gone back to a water pump mounted fan.

[01Konvict]

I got mine installed and I wired the LS1Fans/BB harness up to the 14v ac wire under the fuse panel. However when I turn the ac on none of the fans turn on. I am now troubleshooting the fans and harness to figure out how to activate the fans. I didnt reach 209 for the regular fan to turn on, so I couldn't verify that one either.

[Rivieraracing]

Unless you were told otherwise from Justin, you should hook your 12v wire up to the little red jump box next to the engine bay fuse box, I also attached my grounds to the bracket that holds the jump box!!
As for the AC wire, where did you attach the trigger wire to? There should be a wire loom running vertically next to that red jumper box, that's where I was told to tap into the ac circuit. There were 3 wires in there that looked like they could be the wire I was suppose to find but all three did different things!! One had the fans on all the time, no matter if the ac was on at all. Then the next one didn't trigger the fan on at all, no matter what setting the ac was on, and the 3rd one that I found in that loom ended up being the correct one. Post a pic of where you tapped in for the AC wire if you don't mind and get a chance!

---------- Post added at 06:46 AM ---------- Previous post was at 06:43 AM ----------

Check this link out and look at post #34, the last picture shows where I attached my grounds, tapped into the AC wire, and also if you look the right top of the red box, shows where my power wire is hooked up to as well!!

http://www.tahoeyukonforum.com/forum/showthread.php?t=9400&page=6

[01Konvict]

The power wire is bolted to the red power block and the ground hooked to the power bracket. The #42 pin is inserted into the PCM and the A/C wire is connected to the power wire under the hood fuse panel as posted in Post # 1 of this thread. The green wire I connected provides a +14v when the truck is running and AC is on.

[Rivieraracing]

Well, sounds like you hooked up everything like I did but just with a different trigger wire! Not sure how the LS1 fans are, but i'd guess that each fan has 2 connectors per fan. So if that's the case, I'd unhook the fans from the harness and run a ground wire to one connector on the fan and another separate wire to the other connector to a 12v source (the battery would be perfect) to test each fan out. If the fan comes on, then it's something wrong with one of the connections and/or something wrong with the harness!

[01Konvict]

Good idea as I will try a direct wire from each battery terminal to activate each fan. I will also trace the power wire to the relay and see if it gets power at the relay and where it outputs the voltage if any.

[01Konvict]

Got it figured out!! Both fans work as direct wired to battery. Checked all the wire leads and verified all had the correct voltage. When chasing the wires I discovered a bad relay or stuck relay. It was humming and would not close the switch to activate the ac fan on high. I tapped the relay and got it working. Also I grounded the Pin #42 and activated the temp driven fan. Hope this helps other people out. Also attached is a wiring schematic for the fans.
http://i2.photobucket.com/albums/y28/SnakeOiler/Vehicles/Silverado/Projects/ElectricFans/Truck_Fan_Wiring_3relay.jpg

[Rivieraracing]

Very nice man, glad you got it figured out!! Nice to see someone else that knows how to use a voltmeter!!

[tRidiot]

My fans are working when the A/C compressor kicks in, but due to a direct-wired trigger.

Did not work with the Black Bear harness and a local manual tune. Temp does not trigger, either.

I'm not sure how to fix it... <sigh>. Really don't want to pay a couple of hundred for a BB computer swap when I've already had the programming done and it may not change anything. I've got to figure something out... forgot and left the truck idling last night and when I got back in, the temp gauge was pegged! Dangit! I can't risk that happening again.