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Donor car was a 95 Camaro Z28 that used (3) fan relays for the oem two fan setup, earlier year model only used (2) fan relays.

Installed a Derale 18217 two speed fan which obviously requires the low speed to be activated before the high speed can be tripped.

Derale fan info:
2400/1800 cfm
23.5/17.4 Amps

I assume the (3) relay setup was used to take some draw off the high speed fan relay in the oem two fan setup?

Question: Do you see any concerns using the early (2) relay wiring diagram for the Derale fan? A11 primary and A10 secondary?

Also..anyone know the amp rating for the oem Potter & Brumfield 14100455 relays?

Thanks

Schematic Link:

http://lt1swap.com/pictures/100_1778.jpg

Injuneer

This diagram shows how to wire up for 2-speed operation. Using the two relay setup, use the low speed relay (lt blue wire from PCM to Fan 1 relay) for the relay shown in the diagram (load side to brown wire on fan), and the high speed relay (brown wire from PCM to Fan 2 relay) for a similar relay setup for the load side grey wire on fan)

http://www.jegs.com/InstallationInst.../259-18212.pdf

The factory setup reverses the signal side of the relay. The 12V is supplied constant from fuse 6 in the factory diagram, and the PCM provides the ground. So you would have to wire it that way on the signal side.

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Fred

Have no problem wiring up the fan..probably should have just asked why GM went to the (3) relay setup i.e what was the advantage?

Again..thanks for your help

Injuneer

The stock fans are only 2-wire fans. The 3-relay system achieves two speeds by running the fans in series (each fan only sees 1/2 the voltage) to achieve low speed, and in parallel (each fan sees 12V) to achieve the high speed.

Your fan has 3 wires. The wiring diagram indicates each of the power wires neds 12V to function, so you always need to run the fan with parallel connections to 12V. The fan #1/fan #2 provides that.

It would seem that the dual fan low/high configuration is superior to the fan #1/fan #2 setup, because the fan #1/fan #2 setup only pulls the air through (roughly) 1/2 of the radiator in the fan #1 only mode. But the low/high setup pulls air through (roughly) the full radiator area at all times.

I suspect GM decided is was cheaper to just add a third relay to achieve the low/high configuration that it was to buy two fans with 3-wire connections. Just a guess though.

shoebox

Here is a schematic I made for someone a long time ago that was doing a 2 speed fan. It applies power to low or high one at a time-not concurrently.

4586

Thanks guys..good stuff.