LS Swap - dual fan wiring

[TA_C10]

Been reading posts and articles and of course LT1swap website. Not finding what I am looking for... Can you guys help?

I have dual fans that came with my radiator. They are SINGLE speed fans. The following diagrams on LT1swap.com shows how to wire up either a single speed fan(singular), or dual speed fan(singular).

My question is how do I wire up DUAL fans that are single speed each? My PCM wiring has low and high speed wires to hook up. Do I just choose the high speed from PCM only?






My PCM wiring via LT1swap.com shows I have a low speed and high speed wires to use.
BLUE/GREEN wire harness connectors - 2005 Harness
Is this correct that these are low speed high speed? Or is it just FAN1 and FAN2??

[TooTall]

When you say single speed only, did you mean both on via PCM trigger? If that's the case, then they'll both come on at the same time with 2 relays

If you want them to operate independently, you can have fan 1 come on at high temp, and the other with the A/C trigger.

The best way would to have both fans operate on 2 speeds via the PCM triggered grounds from the PCM:

This can be done with 3 relays. They will function on low and high speed with PCM triggers

[MShip]

Currently researching same thing. This might help?

https://www.lsenginediy.com/upgradin...ric-fan-guide/

[ls1nova71]

The 3 relay set up is the way to go if you have 2 single speed fans and want them to operate on both high and low. https://ls1tech.com/forums/conversio...e-i-m-5-a.html

[First c10]

Originally Posted by ls1nova71

The 3 relay set up is the way to go if you have 2 single speed fans and want them to operate on both high and low. https://ls1tech.com/forums/conversio...e-i-m-5-a.html

This is how I ran both my swaps using the ECM low speed and high speed triggers.
Low speed equal 6 volts dc to each fan (fans spins at 50%)
High speed equals 12 volts dc to each fan (fans run at 100%)

[mongocanfly]

On mine I'm running dual fans..the 2 trigger signals come from the ecm...each goes to a seperate relay ..
The ecm is set for fan 1 to come on at 175deg...fan 2 comes on at 185deg..

[TA_C10]

Guys this is great info thanks. Question. On my PCM wire harness. Its the blue green connector 2005 harness. PINS = BLUE 41, GREEN 33

Do I have these labeled wrong? Should this be:

A) FAN1 and FAN2
or
B) FAN LOW and FAN HIGH

In LT1swap.com pinouts, they say fan1 and fan2, but in his video I'm pretty sure he said low and high. His video is for a 2003 harness PCM but I think they are same as 2005. This is going to be important when choosing how to wire these up.

Another question. What guage wires did you use to wire up these relays?

1. 20awg for triggers?
2. 16awg for grounds?
3. 12awg for power?
4. 12awg for output to fans?

Oh, and what size fuses do these need? 30a for each relay, 40a for each relay? Or something else?

[TA_C10]

Need to open this back up. I'm building my wire diagrams and about to start wiring all this.

3 relay setup:
relay 1 = 40amp fuse
relay 2 = 40amp fuse
relay 3 = 10amp fuse

Can I combine relay 1 and 2 through the same 40amp fuse? Or do they have to have a 40amp fuse per fan?

[MDPotter]

This is the schematic I used (no accommodations for vintage air though). I used (1) 40 and (1) 10.

As far as the Fan 1/2 vs Low/High nomenclature, Fan 1 means low temp trigger (both fans half speed), Fan 2 means high temp trigger (both fans full speed). C1 (blue) pin 42 should be low temp trigger and C2 (green) pin 33 should be high temp trigger.

How do you know that your fans are only one speed? I don't know that I would call my fans "2-speed", they just run half speed because when Fan 1 wire sends a ground trigger, each fan only gets 6V so they only run half speed. When Fan 2 wire sends a ground trigger, each fan gets 12V so they run full speed.

I don't have a good understanding of the schematic, I just know that it works.

I can't tell how you want your fans to function. If you want them to run like GM designed and how most people recommend, use the schematic here. I like this because it cools across the whole radiator all the time and your fans should last longer and it's quieter.

If you want one fan to run full speed when coolant reaches low temp and the other fan to come on full speed when coolant reaches high temp, you can simply use Fan 1 (low) and Fan 2 (high) to trigger each fan through its own relay and fuse.

Trigger wire size doesn't matter, it's just a ground. The wires that came on my cheapo fans are probably 16, but I used larger wires in my fuse/relay block so I can use higher powered fans down the road. I used 8 to feed the buss bar, 10 to feed the fuses and relays 1 & 2, 14 to feed relay 3, then 14 to feed the fans.

[Richard]

Thanks for the diagram will be doing this in the near future. Looks like it just puts the fans in series to slow them down. Curious if the low speed control turns off when high speed comes on. I am guessing it does not due the use of three relays. Personally I would not recommend a setup that only has just one fan on in most dual fan configurations. If there is any sort of shroud and only one fan is running a good amount of airflow will be pulled through the fan that is off instead of through the radiator. Just recirculating the air under the hood. Each fan coming on a different temp may be okay if fans are tight to the rad. But then you are not using the full cooling capacity of the radiator. JMHO

[MDPotter]

I was curious as well - what we did was wire everything up except for the ground triggers and tested that theory. When you ground out only the high fan trigger, only one fan run full speed and the other shuts off. We confirmed after starting it and getting it warm enough that both fans were on full speed, so both the low and high fan triggers are grounded out once you reach the high temp.