Little Help with AC and Cooling Fan Control Strategy

[Nshyster]

I have been reading the various threads here for quite some time and the information from all you folks has been immensely helpful. Now for my problem. I am installing a GMPP LS3 crate engine with a new Vintage Air Gen IV in my 69 Camaro. The engine controller is an E67 ECM. From what I understand I cannot use the E67 ECM to control the AC compressor and fans together so I need another strategy. So I am planning to use the VA trinary switch to turn the fans on but I do not want the fans running full blast all the time. My thought is to do a series/parallel fan setup. The following diagram shows my idea. Not sure what to do about idle bump at compressor start or how to shut it off at WOT yet. But to protect the compressor I am thinking I can put in a rpm window switch to shut the compressor off at a set rpm. To shut the compressor down at WOT is there a signal from the electronic throttle pedal I can tie into? Apprciate any thoughts and comments. What do you guys think?
Thanks for your help.
Bruce L

[Nshyster]

Ooops, attachment didn't. Try this.

[Lous69]

I did not study your proposed schematic. I just wanted to suggest that I believe it is possible to have your E67 control the fans as a function of both the AC pressure and / or the engine coolant temp.

Mikels, a member on this site, is going to reprogram my E67 to do that. He REALLY knows his stuff and he is very good to work with. He has never made me feel stupid no matter how basic my questions have been.

To let your E67 control the fans instead of the VA trinary switch I believe you will need to install a GM AC pressure switch and connect it to your E67. Then you will need to change the AC pressure settings in your E67 cal to compensate for the differences between the GM and VA AC systems.

You would still want to retain and use your VA trinary switch to protect your compressor but the E67 would control your fan(s).

If you want pulse width modulation of the fans (so they only run the speed needed to do the job) you will need to reprogram the E67 from discreet to PWM fan control mode and install a PWM fan controller like the one used in C6 Corvettes.

There is another thread in the engine section that talks more about the PWM control mode option:
https://lateral-g.net/forums/showthread.php4?t=40215

[Nshyster]

Lous69, thanks for the response. I have read thru your thread about PWM to control the fans several times and it seems like a very interesting way to go. I was trying to keep my control strategy a little simpler. If instead of going with PWM can I get the ECM to control my fans thru a low-speed/high speed control architecture driven by a function of the AC pressure and / or the engine coolant temp? If I understand what you are saying the trinary switch turns on the AC compressor with a signal from the VA controller, then the fans turn on or off as required driven by the GM AC pressure switches (low and high) or ECT with the appropriate ECM calibration.

I am still unclear about a few things.

1. Is it possible to get idle bump when the AC compressor turns on?
2. Is there a signal from the ECM to shut off the compressor at a specific rpm or do I still need the normally closed rpm window switch? Several friends do not have rpm protection in their LS installations and have exploded a couple of compressors, literally.
3. Is there a signal to the ECM, maybe from the electronic throttle pedal, that I can use to disable the compressor on WOT?

My research has indicated that I pretty much have to keep the AC compressor control separate from the ECM. So I am curious how you are handling compressor rpm protection and WOT compressor disable in your build with PWM?

Thanks for your help.
Bruce L