There are two signal wires running to the fan relay - one blue and one green. Separate and run each to separate relay for individual fan on/off control.

Or you can run to three relays to have fans work in tandem - as voltage divider for 1/2 speed in series and at full speed in parallel. Sorry away from computer so can't pull up diagrams - but 322V (2009-2014 CTSV) is wired this way.

There is space in panel for additional relays and fuses - just need the terminals to populate vacant locations.

Then the calibration needs to be set up for dual descrete fan drivers.

The parallel / series set up is slightly more difficult, but superior in that both fans run at either 50% or 100% - vs 2 fans either off or on.

Dave

Why wouldn't GM do that from the beginning to have dual fan controls? Instead of moving the blue or green wire to another relay wouldn't it be the same thing is if i took the blue fan wire from the box and split it to two other relays? Only downfall i see here is if the main relay feeding both relays fails neither fan will turn on. The way you are saying seems safer but is it worth it?

Are the two signal wires going to the relay one being a 1/2 speed wire and the other full speed?

What you are talking about is that what PCM of NC is packaging here?

http://www.pcmofnc.com/index.php/per...ectric-fan-kit

I can't answer why GMPP set up that way. Simpler / cheaper likely answer.

Fan outputs are same from ECM. One is FAN1 the other FAN2. Reason you have to use 3 relays to make low/high setup is to make fans a voltage divider (series) or receive equal voltage (parallel). The outputs are same - just a trigger signal for relay (IF set in cal as discrete outputs).

Yes - link you sent is doing what I'm talking about - but you can do yourself for much less than that price. Of course you pay for convenience and can use this prefabed kit to do same without having to research / procure parts yourself.

As far as reliability - current GMPP setup relies 100% on one relay. Splitting runs 2 relays (each independent). Parallel/series runs 3 relays - but is method used by production dual fan GM systems since 1990's. I recommend not 'cheaping out' with electrical parts regardless of method selected.


Dave

Decided to buy the electric fan kit for the gmpp from pcm of nc. I also purchased http://www.pcmofnc.com/index.php/per...ump-circuit-ac Decided to buy the two kits instead of making it myself.

reverse lockout wiring
 

http://www.grcperformance.com/Instru...%20Lockout.pdf

The two wires going to the reverse lockout are simple enough but my question is how to hook up the other two to the VSS. Which one is my vss signal and which is my vss reference? Notice page 8 on the above pdf.

What color are the two wires that hook up from your GMPP harness? Usually it's one light green wire and one purple with a black stripe.

Ill have to look tomorrow again. We hooked one up today and it works great. Really all you need to do is hook up the yellow wire to one of the t56 vss wires. The blue wire is hardly ever used. If it doesn't work you can also just swap the yellow wire to the other wire and not cause any issues.

Is it OK to run Spal fans in a series/parallel arrangement? I'd prefer the three relay two speed configuration over two relays.

Thats what pcm of NC sales. They send a patch to patch into your edu and all the easy connectors to set it up in the fuse box. The AC override acts as a fan bump.
This kit makes use of two temperature outputs in the computer and integrates it with an air conditioning controlled fan speed increase. Turning on the A/C will bump the fan speeds to the next higher speed.
http://i30.photobucket.com/albums/c3.../Scan%204.jpeg

Thanks!