Cooling Fan relay setup

[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

[Hcb3200]

Going to call overthinking on this one.

Yes the PCM has a two fan option.

With the three relays it controls speed

It does this by putting the fans in series on low speed call.

As in

Positive wire ----- fan 1, wire out of fan one to fan two then wire out of fan two to ground. (in reality i think it does the grounds but either way works)
aka sharing power therefore half speed each.

When it calls for high
The relays flip and

Fan one positive direct fan one and wire out to ground

Fan two with a separate positive and wire to ground.
Both fans get full amps and run wide open.

Since you have one fan just wire the fan to the low side of fan one. Low side is always on and hot when pcm calls any fan to run.

Set your PCM to be on when you want temp wise since you are going to remove all the vats and other items anyway. and be done. It will run full speed as long as the pcm calls it to run.

Assuming you do not have a E78 ecm. it runs a mechanical fan and the pcm does not call the fan relays. even though its in the computer and the relays are in the fuse box. Ask me how I know. E38 which is the most standard is relay and pcm fan triggering worthy all day.


I doubt in a old school truck you will ever need two fans even with AC.
It needs the higher speed in modern trucks with a crammed full engine bay not letting out heat. mountains of towing power in modern trucks running full bore AC to multiple systems in some cases. This will tax engine heat etc.

[Hcb3200]

This really spells it out.

[57FleetsideC4]

Originally Posted by Hcb3200

Going to call overthinking on this one.

Yes the PCM has a two fan option.

With the three relays it controls speed

It does this by putting the fans in series on low speed call.

As in

Positive wire ----- fan 1, wire out of fan one to fan two then wire out of fan two to ground. (in reality i think it does the grounds but either way works)
aka sharing power therefore half speed each.

When it calls for high
The relays flip and

Fan one positive direct fan one and wire out to ground

Fan two with a separate positive and wire to ground.
Both fans get full amps and run wide open.

Since you have one fan just wire the fan to the low side of fan one. Low side is always on and hot when pcm calls any fan to run.

Set your PCM to be on when you want temp wise since you are going to remove all the vats and other items anyway. and be done. It will run full speed as long as the pcm calls it to run.

Assuming you do not have a E78 ecm. it runs a mechanical fan and the pcm does not call the fan relays. even though its in the computer and the relays are in the fuse box. Ask me how I know. E38 which is the most standard is relay and pcm fan triggering worthy all day.


I doubt in a old school truck you will ever need two fans even with AC.
It needs the higher speed in modern trucks with a crammed full engine bay not letting out heat. mountains of towing power in modern trucks running full bore AC to multiple systems in some cases. This will tax engine heat etc.

Originally Posted by Hcb3200

This really spells it out.

Thank You for the information. Steve

[fauXGT]

When I eliminated the clutched fan on the '91 GT for intercooler piping, I researched alot of junkyard parts. I realized that there is alot of confusing ways to go. Being my ECU does not have signaling outputs for e fans, I went for a single SPAL 16" fan with a variable speed controller. Has an A/C auto on input and a stand alone temp probe that fits into the radiator, being I'm running a 180* thermostsat for the supercharger. It doesn't matter what temp anything else is running, it only kicks the fan on when it needs to. Hot days when shutting it off, the fan will still continue to run for 30+ seconds after just to cool things down, then turn off. It does vary the speed... not just low/high. 15 years ago $110 for the fan and $80 for the controller/temp sensor. Love it. My 2 cents.

[57FleetsideC4]

Originally Posted by fauXGT

When I eliminated the clutched fan on the '91 GT for intercooler piping, I researched alot of junkyard parts. I realized that there is alot of confusing ways to go. Being my ECU does not have signaling outputs for e fans, I went for a single SPAL 16" fan with a variable speed controller. Has an A/C auto on input and a stand alone temp probe that fits into the radiator, being I'm running a 180* thermostsat for the supercharger. It doesn't matter what temp anything else is running, it only kicks the fan on when it needs to. Hot days when shutting it off, the fan will still continue to run for 30+ seconds after just to cool things down, then turn off. It does vary the speed... not just low/high. 15 years ago $110 for the fan and $80 for the controller/temp sensor. Love it. My 2 cents.

Thank You for your opinion on this. My goal is to let my PCM control the fans. I am just looking for a way to let the PCM know the A/C is on which is a Vintage Air Gen IV system. I have a A/C request wire just need to figure out how to use it. Steve