One notable exception: fuel pump. That's a 12V signal.

DC Controls has a stand-alone PWM that can handle 85A continious. I had to change to an FK55 for the MarkVIII fan since the initial turn-on current was melting the ends of the connector body.

http://www.dccontrol.com/fk85.pdf

I'm learning a ton here. Thanks for the great discussion and info sharing.

Now imagine sitting in a bar listening to a conversation between Mikels and Stielow. :willy: :bang: :willy:

That would be the coolest bar I would have ever been in......

We Engineers think this stuff is intoxicating...we don't need no stinkin bars...

Well OK, in Rolla we did need our bars because there were no women.

I guess we are a pretty sad lot

Hell, I think this was the highlight of my week!

If I missed it it, I apologize. But what compressor are you running? The factory compressor is controlled by the ecm not just at the clutch but it varies the pitch on the vanes right? I didn't think that variable compressor is compatible with the VA unit?

If you are running a sanden compressor then why not leave the ecm out of the equation for the ac? You could run a 5 volt ref to one side of the trinary and from there to the ecm to tell it that ac is on. It would only make when the specified pressure is reached and you could set it to run at, say 40% on the pwm when the AC calls for it.

It really doesn't take that much fan to cool off the condenser. When we charge systems here, the fan only cycles for 8-10 seconds at a time and doesn't cycle again for at least another 90 seconds. You can watch the high side pressure drop quickly, you would swear it had a leak. So in my mind it would be simpler to do it that way and not have to worry about the oem pressure sensor.

In my case, it's a Sanden. I was looking for a solution that doesn't cycle the fan at max speed for 10-15s every 90s... but would run a lower fan speed for longer times. I don't know of any aftermarket fan controller that supports that, so I thought having the ECM do it would be a nice integrated feature.

That is our current thinking too. We are also using the Sanden compressor.
We plan to let the Vintage Air system control the compressor as it is designed and use the ECM control to the fans since it looks like that can work.

So you are trying to eliminate the on/off cycle. If the fan soft starts and runs at half speed for the AC I think it would work. This is really only critical during warm up, I think, once up to temp wouldn't normal fan cycling move enough air to keep the trinary switch out of the loop?