I installed E-fans on my 2001

[ScottyBoy]

UPDATE: After daily driving my Suburban for the past 13 years since my Electric Fan swap, I have had zero issues. Thats over a decade of brutal Louisiana summers, countless road trips, including one trip that was over 3,000 miles total when I drove the family to Orlando.
The Electric fans are working just fine, and the fan harness has held up quite well. I was even in a collision a few years ago, and cracked my radiator mount, but the fans were spared of any damage. Lol.

 

[Sam Harris]

UPDATE: After daily driving my Suburban for the past 13 years since my Electric Fan swap, I have had zero issues. Thats over a decade of brutal Louisiana summers, countless road trips, including one trip that was over 3,000 miles total when I drove the family to Orlando.
The Electric fans are working just fine, and the fan harness has held up quite well. I was even in a collision a few years ago, and cracked my radiator mount, but the fans were spared of any damage. Lol.

One of THE best upgrades for our older GMT800’s!! Thanks to you, and some other members here documenting the process, I couldn’t be happier with the results, and ease of installation.

 

[Marky Dissod]

One of THE best upgrades for GMT800s!
Thanks to you, and some other members here documenting the process, I couldn’t be happier with the results, and ease of installation.

Every GMT800 extant should be maintained with the following GM OE UPDATES:
GM OE 2006 KW1 Alternator
GM OE 2006 Electrical Fans Update
GM OE 2010 Front Brake Caliper & Rotor Update

 

[mattbta]

Every GMT800 extant should be maintained with the following GM OE UPDATES:
GM OE 2006 KW1 Alternator
GM OE 2006 Electrical Fans Update
GM OE 2010 Front Brake Caliper & Rotor Update

How do you convert from 4 pin to 2 pin alt?

 

[Matthew Jeschke]

Sweet dude. Thanks ordering screw!

 

[Matthew Jeschke]

Complete with upgrade. I have a few notes... but first.

WOW you did an AMAZING job refurbishing the junction block! It was LIKE NEW. I was going to have to resort to eBay to do this project but you saved me all the grief of fiddling around, cleaning up, and rebuilding the harness. Thanks!!!

I got the high speed fan control to work

Wiring

C2 Pin 33 is AC Recirc mode on the 2001, on the 2005 it's high speed fan control.

DON'T cut the wire... de-pin it from the harness. It's going to be a green wire. Then tuck it up in the wire loom incase you want to revert to AC recirc mode.

Next populate that pin with a blue wire.

Track the PCM wire loom up into the junction block. I like to maintain factory routing.

I made another wire connect to the AC relay as shown in image below. Then it connects through the two pin connector (the other contact being for low speed fans).



Tuning


these are settings from 2001. Change the Recirculation fitted setting to "Fan #2".

This switches the DIO in the PCM to logic for fan instead of logic for Recirculation. Note the recirculation door seems to still work. However, I think there's a boost pressure mode for the AC. I've not quite figured it out. Whatever it is it's now disabled. If anybody knows more about "Recirculation Fitted" mode... Let me know I'd be interested to understand what I disabled.

Additionally, you CANNOT splice into the recirculation wire and onto the relays for fan control. This divides the voltage and the relays won't trigger.

I believe but couldn't confirm that the setting below that "Type Fitted" if changed to "Serial Cycling" may also read the pressure. You could in theory then divide the reference voltage in half and send it to PCM (Pin 14 C2? double check, this is from memory) and get the fans to kick on when AC is enabled. However, at this point the truck died, so I gave up on testing that theory. FYI ~ I kept blowing fuses, and draining the battery testing all these theories so may have been due to something else that truck wouldn't start. 100% sure even if truck did start that serial cycling control process won't run an analog cycling AC.

A note on the low speed trigger wire @Scottyboy did this part for me.

C1 Pin 42 is not populated on the 2001, on the 2005 it's low speed fans.

Populate that with a green wire (@ScottyBoy) did that for me already.

Make the wire long enough to trace the PCM harness back through and into the junction block.

Take these two wires and put them into a two wire connector. (I more or less revised @ScottyBoy's harness to do this).

A note on the AC clutch relay connected to B3 clutch supply voltage

It maybe prudent to put a slightly higher gauge wire on there. Say 14 gauge. Reason is, that's a 10 amp circuit. Granted the AC clutch is something like 6 ohms so most of the current should flow through it... but if there's a fault, say the coil in the relay for the fans shorts out it won't fail safe. That small gauge wire could heat up a bit before the fuse ever pops. It's splitting hairs but failure mode could result in a burnt junction block or worse a fire.

Possibly revise trigger for AC fan mode

I'm only saying this because I studied the factory service manual for hours trying to optimize things. I think I may have come across a wire possibly available under the hood that / PCM pinout even that indicates if the AC is commanded on. That would be better as the AC clutch isn't always on when the AC is on. This causes the fan to cycle quite a bit which isn't ideal for hardware. Will it tolerate it? Yeah probably fine... but will it last as long that way... most likely not. It'll prematurely wear out the harness and fans themselves due to spike in current every time the fans go on and off (it's literally a electrical wave in the wire).

Back to relays...

Typically relays have the control side (coil) on a separate / isolated circuit to help protect the delicate control systems. I see even GM isn't doing that now in this fan design. I digress though...

I think that's about it. I fiddled with this from sun up till sun down two days in a row. In short, it'd be a good case for a stand alone fan controller. GM got super janky with this PCM. It shouldn't have an AC controller... that should be in the head unit for the AC if at all. AC takes a couple switches to run and that's about it.

I digress again... lol hard to suppress my engineer brain. I've done a bit of design work like this but for aircraft.

 

[ScottyBoy]

Complete with upgrade. I have a few notes... but first.

WOW you did an AMAZING job refurbishing the junction block! It was LIKE NEW. I was going to have to resort to eBay to do this project but you saved me all the grief of fiddling around, cleaning up, and rebuilding the harness. Thanks!!!

I got the high speed fan control to work

Wiring

C2 Pin 33 is AC Recirc mode on the 2001, on the 2005 it's high speed fan control.

DON'T cut the wire... de-pin it from the harness. It's going to be a green wire. Then tuck it up in the wire loom incase you want to revert to AC recirc mode.

Next populate that pin with a blue wire.

Track the PCM wire loom up into the junction block. I like to maintain factory routing.

I made another wire connect to the AC relay as shown in image below. Then it connects through the two pin connector (the other contact being for low speed fans).

View attachment 453290

Tuning

View attachment 453289
these are settings from 2001. Change the Recirculation fitted setting to "Fan #2".

This switches the DIO in the PCM to logic for fan instead of logic for Recirculation. Note the recirculation door seems to still work. However, I think there's a boost pressure mode for the AC. I've not quite figured it out. Whatever it is it's now disabled. If anybody knows more about "Recirculation Fitted" mode... Let me know I'd be interested to understand what I disabled.

Additionally, you CANNOT splice into the recirculation wire and onto the relays for fan control. This divides the voltage and the relays won't trigger.

I believe but couldn't confirm that the setting below that "Type Fitted" if changed to "Serial Cycling" may also read the pressure. You could in theory then divide the reference voltage in half and send it in Pin 14 C2? and get the fans to kick on when AC is enabled. However, my truck wouldn't start with that setting and I'm quite positive the AC wouldn't work even if it had...

A note on the low speed trigger wire

C1 Pin 42 is not populated on the 2001, on the 2005 it's low speed fans.

Populate that with a green wire (@ScottyBoy) did that for me already.

Make the wire long enough to trace the PCM harness back through and into the junction block.

Take these two wires and put them into a two wire connector. (I more or less revised @ScottyBoy's harness to do this).

A note on the AC clutch relay connected to B3 clutch supply voltage

It maybe prudent to put a slightly higher gauge wire on there. Say 14 gauge. Reason is, that's a 10 amp circuit. Granted the AC clutch is something like 6 ohms so most of the current should flow through it... but if there's a fault, say the coil in the relay for the fans shorts out it won't fail safe. That small gauge wire could heat up a bit before the fuse ever pops. It's splitting hairs.

Possibly revise trigger for AC fan mode

I'm only saying this because I studied the factory service manual for hours trying to optimize things. I think I may have come across a wire possibly available under the hood that / PCM pinout even that indicates if the AC is commanded on. That would be better as the AC clutch isn't always on when the AC is on. This causes the fan to cycle quite a bit which isn't ideal for hardware. Will it tolerate it? Yeah probably fine... but will it last as long that way... most likely not. It'll prematurely wear out the harness and fans themselves due to spike in current every time the fans go on and off (it's literally a wave in the wire).

Back to relays...

Typically relays have the control side (coil) on a separate / isolated circuit to help protect the delicate control systems. I see even GM isn't doing that now in this fan design. I digress though...

I think that's about it. I fiddled with this from sun up till sun down two days in a row. In short, it'd be a good case for a stand alone fan controller. GM got super janky with this PCM. It shouldn't have an AC controller... that should be in the head unit for the AC if at all. AC takes a couple switches to run and that's about it.

I digress again... lol hard to suppress my engineer brain. I've done a bit of design work like this but for aircraft.

I see what you're saying about constantly cycling when the AC clutch is engaged. And yes, I can confirm that DOES indeed happen, because my fans are wired to the AC clutch. In colder or extremely humid weather when I have the defroster running, I can hear my fans CONSTANTLY kicking on and off. By constantly, I mean as often as every 20 seconds or so. 20 seconds off, then kick on for 20 seconds, and on, and on and on. Sometimes it runs a bit longer, more like a minute or two. But it's quite annoying when it does that, because if it at night I see my lights dim every time it kicks on.
As far as it affecting the lifespan of the fans, I have had my fans wired like this since 2011. Look at the date I originally wrote this install thread, it was 2011!! Do I have been daily driving my truck with the fans wired like this for a solid 14 YEARS now and everything has held up quite fine. Even with the nonstop cycling sometimes when I'm running the defroster instead of the AC. I've driven my truck on countless road trips over the years including a 3,000 mile trip to Orlando with my family. Since my wife recently bought a Chevy Traverse which has just as much interior room but is FAR better on fuel, we take that on road trips now. So my Suburban is mostly for me just commuting to work now, which is about 27 or 28 miles each way. I'm still running the same fans, same harness and same AC compressor and clutch that was on my truck in 2011. For full Disclosure, I DID have one of the fan relays fail sometime around 2017 or 2018 I believe. I noticed my temps were running a bit high, so I checked the fans, realized they were not coming on. After some quick troubleshooting with my PowerProbe, I realized that one of the relays went bad. I simply replaced it with another (as I always have these relays on hand because I refurbish and sell these fan harnesses) and everything was fine after replacing that relay. And everything has been fine ever since. So take that for wgat it's worth. Thats just my personal experience, that doesn't exactly mean your fans and harness will last at least 14 years. But in my opinion, they mostt likely will. These OEM harnesses are built like tanks. I have seen DOZENS of threads all over various forums about people having issues with aftermarket harnesses overheating and melting wires, relay plugs, or relays themselves, or ALL of the above. So far, I have never seen an OEM cooling fan harness melt. Just a failed relay. But then again, I've seen these same type of relays fail on anything from a fuel pump, to headlights, to a horn. So..........

 

[Matthew Jeschke]

You did a beautiful job on the harness. I keep going back looking at the junction box and harness wishing you lived closer. I'd hire you to do more work on my truck

Good to know about fans... It seems the relays are the weaker point. GM must have done a good job beefing up the fans so they don't fail. Kind of makes since as a fan failure could result in an engine failure.

If I can find the time I may design a stand alone fan controller. I have a stack of microcontrollers from work in my office. All I need is coolant temp (could possibly splice into existing sensor) and something to say AC is on, perhaps clutch signal again. There maybe even cheaper / simpler ways to build it but I could wire something up in a few hours with a microcontroller and test it.

 

[Matthew Jeschke]

I missed something... I'D NOT put the supply line to the stud on the junction box. It's 80 amps fused for fans, yet the stud is fused for 30 amps. I went to go for a drive today and it blew the fuse several times. I put a breaker in there to diagnose and dawned on me, you need to supply voltage straight off the battery for the fan relay box.

You might be able to get by with the stud, though I'd not recommend it. I bought the biggest fans you can purchase (from GMT900 6.2L engine). I moved red fan supply wire over to the positive post of the battery. Seems to have resolved the issue.

 

[Rocket Man]

Yeah I just did mine in an hour and it’s been fine for years. I’m sure it will outlast everything else on the truck,. I just can’t see myself getting that involved in a fan. There’s only so much time in my life and many many other things I’d like to spend that time on. Keep up, though- you might one day solve whatever problem you’re trying to solve. My eyes get all glassed over about the second paragraph of your posts.