Cooling Fan relay setup

[57FleetsideC4]

Hi all, I have a new question 0n my LS 57 pickup project. I want to run the one 16" fan I am using with 2 speeds off of fan 1 and fan 2 from the PCM. It looks like typically there is a 2 fan 3 relay setup that runs the fans on low speed by running the fans on a series circuit. I want to run the same 3 relay system with a resistor instead of a fan to slow down the one 16" fan I will be using. Does this seem like it would work? Thank You Steve

[Rickysnickers]

I am going to move your question over to the LS swap area. I think you might get more views there.

[mongocanfly]

Why not just run a 2 speed fan?

[57FleetsideC4]

Originally Posted by mongocanfly

Why not just run a 2 speed fan?

I already had the fan but will look into it. Thank You Steve

[mongocanfly]

Ok, understand, didn't know you already had one

[Joyridin]

I don't see why it wouldn't work. You are going to need a pretty hefty resistor though. The reason GM uses the series wiring is to avoid a resistor due to the high amperage. That resistor is going to get mighty hot.

[57FleetsideC4]

Originally Posted by Joyridin

I don't see why it wouldn't work. You are going to need a pretty hefty resistor though. The reason GM uses the series wiring is to avoid a resistor due to the high amperage. That resistor is going to get mighty hot.

Yes has to be rated high and will make some heat. I found a gm resistor with a fan plug on it just can't get any specs on how many ohms it is. Steve

[1project2many]

GM has used the same 2 speed design in the past. BMW and Mercedes have done it also. One version of the GM fan resistor is P/N 94812213. You could also use a ballast resistor from an old points system. Your truck probably had one on the firewall.

[Joyridin]

Originally Posted by 1project2many

GM has used the same 2 speed design in the past. BMW and Mercedes have done it also. One version of the GM fan resistor is P/N 94812213. You could also use a ballast resistor from an old points system. Your truck probably had one on the firewall.

What was that resistor used on? It is showing 17.25 watts. If I take a 16" Summit fan and look at the amperage, it is 12.9 amps. So..

Wattage = Volts x amperage
154.8 watts = 12 volts x 12.9 amps

The Mishimoto 16" fan draws 7.18 amps. So..

86 Watts = 12 volts x 7.18 amps.

Wouldn't that resistor smoke in like 5 seconds, or am I doing something wrong?

[Jason Banks]

I think you are right Joyridin.

I think the solution is to get a resistor that is equivalent(or close) in resistance to the fan. That should give you 1/2 voltage to the fan.

To find the resistance of the fan, you would divide the voltage by the amp draw.

In your 16" summit fan example, for simplicity lets say 12.9V divided by 12.9A = Fan has 1ohm resistance.

At this point I'm not sure on figuring out how many watts the resistor would need to be. I feel like a 100w resistor would work, but the math might say 154w(or 167w at 12.9v) or 200w for simplicity. Someone that remember more electronics math than me can hopefully come along and explain. I think since you are doubling the resistance your wattage is halved. But it may be quartered across that resistor. Help....
----
I'm back after some googling and at 12.9v with 2ohms of resistance, your at 1/2 the wattage so about 83.2 watts. I'm lost again at figuring out of you only need 1/2 of the 83.2 watt rating for the resistor.

A 200w is almost 4 inches long - https://www.amazon.com/dp/B08G8JGW1M...d_i=B08G8JGW1M

Here a 100w - https://www.amazon.com/Comidox-Alumi...77ZMFZM6/?th=1

Or a 50w and see if it smokes - https://www.amazon.com/LM-YN-Wirewou...dp/B0728B8XQR/

[LeesTruk]

Why don't you try a DRL resistor. Toyotas and Subarus used them to reduce power to their headlamps for DRL's. If you have a u-pull-it yard in your area, I'm sure it wouldn't be cost prohibitive, and most have a 2 wire connector for power in/power out applications

[57FleetsideC4]

Lots of great information guys. The resistance on the fan is 1.5 ohms. The specs say it draws 18.5 amps. I am looking at all types of resistors in that range now. I will get it figured out. I am a little ways away yet on that part of the project. Just looking ahead at what I will need. Thank You Steve

[Hcb3200]

Until you get it worked out or find out if two speeds are even needed.


I run a big 6.0 LS in the 1956 with stock radiator and have AC in it.

Fan is turned on when i want it to manually or comes on automatically with temp switch if its gets hot and I am not paying attention when I need it.

Running no AC and just driving and sitting for short period it barely hits 200 with all that room in truck not much gets trapped. And rarely runs.

In the summer GA August heat at 100+ humidity way up and AC running it will start to over heat without a fan.
But otherwise its off until it comes up to temp and on when it gets to 195/200 temp start temp. If its cool enough outside it will cut off when driving and sometimes off when sitting. Hwy driving it drops to 188 to 195 and has a hard time getting over 200 unless I am pushing it hard uphill.

LS motors like a higher temp (really the computer and all its calculations does) at least all my modern ones do.

Fan is really only for sitting and not forcing air when driving and on highway then even less needed.

Any way ON/OFF one speed is a option.

Clay

[57FleetsideC4]

Originally Posted by Hcb3200

Until you get it worked out or find out if two speeds are even needed.


I run a big 6.0 LS in the 1956 with stock radiator and have AC in it.

Fan is turned on when i want it to manually or comes on automatically with temp switch if its gets hot and I am not paying attention when I need it.

Running no AC and just driving and sitting for short period it barely hits 200 with all that room in truck not much gets trapped. And rarely runs.

In the summer GA August heat at 100+ humidity way up and AC running it will start to over heat without a fan.
But otherwise its off until it comes up to temp and on when it gets to 195/200 temp start temp. If its cool enough outside it will cut off when driving and sometimes off when sitting. Hwy driving it drops to 188 to 195 and has a hard time getting over 200 unless I am pushing it hard uphill.

LS motors like a higher temp (really the computer and all its calculations does) at least all my modern ones do.

Fan is really only for sitting and not forcing air when driving and on highway then even less needed.

Any way ON/OFF one speed is a option.

Clay

Thanks for the information. The pcm has fan 1 and fan 2 outputs and thought it would be quieter. It looks like fan one turns on at 210 and fan 2 at 220. Not sure how to tell the pcm when the ac is on. There is a ac request input but not sure if is seeing a ac request or putting out a ac request. I am sure I am over thinking this but this is my process. Steve

[IIGW]

Originally Posted by 57FleetsideC4

Hi all, I have a

steve look into the fan controllers by The Auto Cool Guy.

i use them when i dont want the ECM to run my stuff.

if the engine needs 20% fan thats what itll get.
if it needs 35 or 55% itll get it..

if you click on the ac itll go 100%

https://www.autocoolguy.com/

[Joyridin]

Originally Posted by IIGW

steve look into the fan controllers by The Auto Cool Guy.

i use them when i dont want the ECM to run my stuff.

if the engine needs 20% fan thats what itll get.
if it needs 35 or 55% itll get it..

if you click on the ac itll go 100%

https://www.autocoolguy.com/

I use one of these. It is a killer set-up. I just assumed the OP was trying to use some type of factory set-up instead of an aftermarket deal.

I have mine controlling dual 16" fans. I think they come on at 185 degrees and slowly increase as the engine heats up. When the AC kicks on with the trinary switch, they come on full blast.

[IIGW]

Originally Posted by Joyridin

I just assumed the OP .

well good sir, you know what they say about those who assume?

[57FleetsideC4]

Originally Posted by IIGW

steve look into the fan controllers by The Auto Cool Guy.

i use them when i dont want the ECM to run my stuff.

if the engine needs 20% fan thats what itll get.
if it needs 35 or 55% itll get it..

if you click on the ac itll go 100%

https://www.autocoolguy.com/

I am trying to use the PCM as the controller as it has 2 outputs for it. Thanks Steve

[jgrote]

You may want to talk to the guy that runs LT1swap.com. He is incredibly knowledgeable about this, and he knows which pcm will do what you are asking. His website is a mess, bit all the info is there.

[57FleetsideC4]

Originally Posted by jgrote

You may want to talk to the guy that runs LT1swap.com. He is incredibly knowledgeable about this, and he knows which pcm will do what you are asking. His website is a mess, bit all the info is there.

Thank You I will check it out. I am going with the 3 relay setup. Steve

[87chevy.com]

I think the best option without putting some janky resistors that sole purpose is to get hot just to acquire a low speed....

I would just install a pusher fan in front of the radiator and wire the 2 fans just like an LS1. You will get both fans on at 1/2 speed for LOW and both will be at full speed for HIGH.

This is the relay box I use when I did fan harness'

Just a quick google search shows this link, the box is good quality, not amazon quality, uses quality seals and terminals.

https://ceautoelectricsupply.com/pro...aterproof-pdc/

clint

[57FleetsideC4]

Originally Posted by 87chevy.com

I think the best option without putting some janky resistors that sole purpose is to get hot just to acquire a low speed....

I would just install a pusher fan in front of the radiator and wire the 2 fans just like an LS1. You will get both fans on at 1/2 speed for LOW and both will be at full speed for HIGH.

This is the relay box I use when I did fan harness'

Just a quick google search shows this link, the box is good quality, not amazon quality, uses quality seals and terminals.

https://ceautoelectricsupply.com/pro...aterproof-pdc/

clint

Thanks for the input on this. Still figuring everything out. Close on a solution. Steve

[Rich84]

I used the factory 3 relay with wire harness and fans off of an Escalade. Made it super easy. Plug and play.

[kglowacky]

rich, what year escalade did you get the setup off of.

[Rich84]

I believe it was 05-06..You can kinda see the relays in this photo at the bottom.
I also used the radiator.