ching0n

I'm wondering if any two fans will work in 2 speed mode using the PCM control (using 3 relay method). Seems like it's wired in series or parallel depending on cooling demand? In other words, the GM fans are not some fancy 2 speed fans but a simple 2 wire (per fan) rig?

Using some mishimoto China clone for a swap

1 FMF

iTrader: (1)

the PCM grounds 1 or both of the fan relays, not the fans directly. so you can wire anything you want off the load side of the fan relay(s)... it won't hurt the pcm.
Only way you could hurt the pcm is if you used different relays where the switching side of the relay that the pcm connects to has lower resistance and draws too much current.

but as for the fans, or whatever you want to wire off the load side of the fan relays, as long as they don't draw more current than the relays are rated for then you are fine, otherwise you'll burn out the relay in the fusebox.

no the oem gm fans do not have a fancy 2 speed motor,
they get low speed by how the pcm grounds only 1 relay, which electrically feeds 12v power to the positive lead of one fan and the ground from that fan goes to the #3 double pole relay which connects it to the positive lead of the other fan, thus running fans in series at 6v each {half power => half speed}. for high speed fans the pcm will ground the control side of two relays not just the one, then positive lead of each fan gets 12 volts and ground lead of each fan goes to ground, running them in parallel where both get full power = high speed

ching0n

Thank you, I gathered as much. I'm just wondering if operating between 6-12 volt is standard practice for most auto fans (or the setup I'm looking at).