As a finishing touch to my efan wiring setup I installed another relay that the fan triggers and grounds the ECU signal previously used by the AC unit.
Thus, the ECU cranks up the BAC and raises the idle to accommodate for the extra electrical load.
Works quite well, the idle jumps to about 900rpm when the fan is active.

I was wondering if anyone knew exactly how this works.
Does the ECU have some internal value it consults depending on the trigger signal it receives?
In other words, if, instead of using the AC signal I used the signal from the power steering input, would the ECU raise the idle more/less or wouldn't it matter?

Just curious.

 

ive often wondered how this is accomplished also. if for examp[le there are multiple loads from diffrent accesories. many have triggers to the ecu. i wonder if they add up and increase fuel/timing of if if one being on has the same effect as many. with my pfc it uses 3 categories for no load, electrical load and a/c which taise and lower the idle. i think tyhe factory system is similar.

 

When the ECU sees the AC is on, it advances the timing from -5...-20 to advancing it to +10...+10 for Lead and Trail timing. Along with the volume increase by the BAC.

PS increases, at idle, to 2.5*L and -5*T at Idle. Along with the volume increase by the BAC.

I doubt the timing is effected when driving by the AC or PS

Series five FSM, Fuel and Emissions has a chart showing what is effected by what. Called the Relationship Chart.

 

Aha, so there is a different amount of compensation applied, dependent upon the expected load.
Time to string a wire over to the PS pressure switch connection and see how that works when the fan kicks on.
Thanks.

 

Update.
I switched from the AC to the power steering ECU input and it works much better.
When the fan kicks on the idle increases only 50 or so RPMs...it's almost seamless.

I'll drive a day or two just to make sure but right now this appears to be the way to go.

 

Hey while you are at it, what happens if you connect the fan to both inputs? Does one cancel the other or are they additive? Is it possible for you to give it a try?

I get a stumble when the compressor kicks in because the fan also kicks to high speed at the same time. If I unplug the fan, the a/c load is compensated for pretty nicely. Thinking of adding the fan input to the P/S just for smoothness.

 

I would imagine that the values for the heaviest load- i.e., the AC- would prevail but I can give it a shot and see.

 

Alright Jack, gave it a shot.

One of two things happened...not sure which.

The car behaved as it did with just the AC input connected. RPM rose about 150 when fan activated.
Given the relative inaccuracy of the tach- especially at low RPMs- and the subtle increase of just the PS input, it's possible that using both ECU signals was "additive" and I just couldn't see it.
I tend to doubt it.

I'm back to just the PS input, need to drive at night with lights and confirm that the idle remains fairly constant.

The only advantage of the original setup was that I could tell when the fan was on but having made it through the summer with no cooling issues, I'm about ready to stop obsessing and just ignore it.
It works- works well, in fact- and I can probably find something else to agonize over.

 

Ok, thanks for the results.