robin427

I'm still a little confused as to what outputs the PCM gives the fans.

On the PCM there is a high speed output (RED 33) and a low speed output (BLU 42).

When the temperature of the engine is low, I assume the low speed output is switched (to earth?).

When the engine temperature gets high, I assume the high speed output is then switched, but what happens to the low speed? Does it stay on or turn off?

I am not going to be using variable speed fans, I am devising a circuit to drive just one fan (low temp.) or both (high temp.). I just need to know what happens to the low speed output - does it remain on or turn off?

Scooter70

iTrader: (1)

I am only using the "low" curcuit to drive my twin Flex-a-lite 220 fans. I have them set to come on at 200*F and they stay on until the temperature comes down to under 195. They don't turn off when the "high" fan (which nothing is hooked up to) is supposed to come on. The stock turn on temps are very high (~229*F for the low temp fan), so you will probably want to edit them with something (HP Tuners, LS1Edit, etc).
Hope that helps.
-Matt

robin427

So it sounds as if when the engine is "cool", only the low signal is switched, but when the engine is "hot"... both are switched - I think that makes my life a lot easier.

Thanks!

slow

iTrader: (7)

correct, low is 1, and high is both

Ryan

robin427

Thanks, guys.

Slow, I've still got that grommet for you if you need it...

slow

iTrader: (7)

yes i do, let me know whenever you make it to the states/orlando and i'll find time to pick it up, or just let me know if you want to ship it.

Ryan

55chevy

iTrader: (6)

Matt, Are you using one or two relays for the dual fans? I look at your cooling page but I don't think you were through with the wiring. Thanks,
Steve

Scooter70

iTrader: (1)

Just one Painless relay that I got from Summit. The fans are wired together so they're controlled by that one relay that gets its signal from the "low speed" fan signal from the PCM. As soon as the temp hits 200, they kick on and bring it right down. I had no issues sitting in pre-Woodward Dream cruise traffic last night.

-Matt

70 LS1

iTrader: (1)

The factory uses 3 relays for the two fans. When cold, both fans are wired in series and run in slow speed. When hot, the fans are wired in parallel and run in fast speed.

I wired up mine per the factory manual and have had no problems. If anyone is interested in a schematic of the 3 relay, 2 speed fan setup, let me know.

crainholio

iTrader: (2)

I did mine the opposite of Scooter's idea, two relays (one for each fan) and both being switched by the PCM's high-speed controller.

I was worried about using the PCM's low-speed controller, as it appears to cycle the relays on/off at some predetermined frequency to make the fans spin slower. In my case I'm using older mechanical relays from a '88 Camaro parts pile, not the spiffy newer relays the LS1 fuse/relay panel had.

I wasn't sure the older relays would work reliably being cycled that way, so I used the high-speed controller which just holds the relays closed until the off temp is reached.

70 LS1

iTrader: (1)

The relays do not cycle to spin the fans slower. The PCM low speed output will go low and ground the slow speed relay. Like I said above, this wires the fans in series giving only 6V to each fan making them run slower.

When the PCM high speed output goes low it grounds the fast speed relays which wires the fans in parallel giving 12V to each fan making them run faster.

crainholio

iTrader: (2)

I stand corrected, thanks much. I evidently got hold of bad info back when I was planning my swap and just committed the sin of propagating it.

I pulled the '01 Helms down and looked at the schematic, and I'm glad I didn't try to reproduce it for my swap either way.

It does, however, look like a good future mod for me would be to wire the low-speed fan control to one fan relay, and have the high-speed control manage the other fan relay...similar to the way my old '90 TPI ECM did.

Set the low-speed fan on/off temps to 195/190 and the high-speed fan on/off to 205/195 and I'm back in the primary + aux cooling fan business instead of spinning up both simultaneously.

robin427

I'm going to wire one fan to each relay but wire in an override switch that will turn both fans on regardless of temperature. I need to wire a diode into the circuit for this, but that shouldn't be a problem.

I have wiring diagrams if anyone is interested...

SnakeOiler

iTrader: (6)

Yes, I would be very interested in this schematic. Do you hook into the A/C as well?

robin427

No, I'm putting the lump into an open top kit car and if you've ever been to Britain you'd know that AC isn't really a vital component!!

Here is my entire schematic. It's made with a program called ExpressPCB (www.expresspcb.com, I think). It should be self explanatory how the fans work. If not, I can do a separate version for you...

70 LS1

iTrader: (1)

Here is the Schematic of the way GM does it. one relay energizes running the fans in slow (series). Then all three energize to run the fans in fast (parallel). The optional wire running to a toggle switch then to ground will allow you to turn on the fans in slow from the dash.

robin427

I'm not using original fans so not sure if they would like being run with 6V... it's a neat way of doing it, though...

keith mccaslin

Please send to me if you still have it.

G Atsma

Please check post dates. Poster you quoted hasn't been here for ten years.
Hit Google for the 2-speed fan wiring diagram. You should find it.
Check post #16. It is right there....

keith mccaslin

Sorry, didn't pay attention to the dates.
Thank you