Controlling the fan with GMPP ECU

**TnBlkC230WZ** · 05-22-2011

I have an LS3 eRod engine and ECU. The car also has a Vintage Air gen IV system with a trinary switch installed. I can't find and input for the GMPP ECU to tell when the AC is running. My dillema is; how to tell the ECU to switch on the fan. Should I just tap into the the fan relay that's in the GMPP fuse panel. If so, do I trigger it on the ground or positive side of the relay?

Is it possible the engine senses the extra load and turns on the fan when the AC is on?

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**garys 68** · 05-23-2011

There really is no good way to give an AC request to the ecu in engine swap from cars that had AC. Not sure if it's even possible with the eRod.
I've done a 5.3 and 6.0 swap, no problems with the AC being on.
As for fan wiring your ecu will ground the fan relay based on temp. In addition, you can ground that same relay through the trinary switch. That's how I did it on both my AC setups, works great.

**parsonsj** · 05-23-2011

Originally Posted by Gary

There really is no good way to give an AC request to the ecu in engine swap from cars

Most aftermarket ECM do have support for an AC request line. FAST, BS3, and Holley all support it.

But if you are using the GMPP ECU (a MEFI-4, I believe) it doesn't have such support. You'll have to hope the ECM can keep the idle speed adequate when you turn on the AC.

**TnBlkC230WZ** · 05-23-2011

Thanks guys. Sounds like an easy fix. I'd think the DBW will keep the idle steady. But I thought the FAST system would keep it steady and I was wrong.

**dontlifttoshift** · 05-23-2011

It will be fine, the ecm doesn't care if the AC is on, its just looking at rpm. The DBW will compensate just fine. We did an Erod in a 70 chevelle with Vintage air iand it was no problem.

**parsonsj** · 05-23-2011

Originally Posted by Tn

I thought the FAST system would keep it steady and I was wrong.

Did you run the AC request through the ECM?

**JMitch19** · 05-25-2011

I have one of these. It is a new product. So far it been a very nice unit. It also offers multiple fan speeds.

http://cgi.ebay.com/ebaymotors/ws/eB...STRK:MESELX:IT

**parsonsj** · 05-25-2011

I'm a big fan of those kind of controllers... the only thing I didn't see was an A/C override. An A/C override and a trinary switch is a slick setup.

**JMitch19** · 05-25-2011

Originally Posted by parsonsj

I'm a big fan of those kind of controllers... the only thing I didn't see was an A/C override. An A/C override and a trinary switch is a slick setup.

I actually hooked my trinary switch to the ECU/PCM low speed input. The nice thing about Easy Performance (the company that makes that product) is that they are small enough to do some custom stuff for you at little to no extra charge. A LSx ecu sends a 12v signal to turn on the fans and that is how the controller is set up default(no relays needed). The trinary switch from VA completes a ground. I asked Easy Performance if they could make me a controller that would work with what I wanted to do and they said no problem we just need to change a few lines of code. I know Easy Performance isn't a sponser here, but Speed Inc retails their products. They have been around the 3800 scene since the begining and are just starting to branch out more I believe.

**Dr.Corvette** · 05-26-2011

I had the same problem. I have a 59 Vette using an LS3 with the GMPP computer and wiring harness. I just tapped the relay like you were thinking. To tap it I opened up the relay-fuse box and soldered a wire to the ground side of the relay. I think it was terminal 85. If you check it with the key on you will find one is hot. The only caveat is I haven't tested it yet. I will do that tomorrow and report back.

**icemanrd19** · 11-28-2015

so to confirm. the gmpp ls3 kit doesnt really need to know if the AC is on or not? Once the AC kicks on the controller will automatically detect load and compensate?

Also to wire the fans....

Run the trigger wire from the fuse box of the gmpp kit directly to the dual fans? This will turn both fans on when the engine gets to hot. Then run a trinary switch from the ac compressor to the 2nd fan that if the engine isnt hot enough but the AC is on the one fan turns on? This would allow a dual fan on when engine is hot and a single if the engine isnt hot but AC on... Is this correct?

**workng247** · 12-13-2015

Check out PCM of NC, they have a kit for the GMPP controller to run dual fans at 2 speeds and a circuit to tie in A/C request. It involves adding a couple relays and some terminals and wires to the fusebox as well as a patch to the PCM. You can do all or part or send it to them. I installed the hardware and sent them the PCM for the patch. Haven't got it running yet, hope it works! lol

A/C request circuit works off compressor run signal so no need for trinary, just binary and interacts bumps fans up when on.

**icemanrd19** · 02-24-2016

Originally Posted by workng247

Check out PCM of NC, they have a kit for the GMPP controller to run dual fans at 2 speeds and a circuit to tie in A/C request. It involves adding a couple relays and some terminals and wires to the fusebox as well as a patch to the PCM. You can do all or part or send it to them. I installed the hardware and sent them the PCM for the patch. Haven't got it running yet, hope it works! lol

A/C request circuit works off compressor run signal so no need for trinary, just binary and interacts bumps fans up when on.

I i installed there dual fan kit and all i have to do is now download the new software. Very simple to do.

Now how do i get this to work? http://www.pcmofnc.com/index.php/per...ump-circuit-ac

I need to look at the instuctions closer. My guess is there is the 3 wires. Light blue, blue and green. Find the blue and green 18g wires going to the GMPP fuse box. Cut them and put this in line with it. The Light blue wire goes to the ac compressor and black goes to a body ground.

**icemanrd19** · 12-07-2015

bump

Any help?

**dhutton** · 12-08-2015

A trinary switch cannot drive a fan directly. You will need to add another relay.

Here is one option:

http://www.ebay.com/itm/Painless-Wir...5Tn1k8&vxp=mtr

Don

**icemanrd19** · 12-15-2015

http://www.gm-efi.com/news/pcm-ncs-g...ctric-fan-kit/

seems interesting. Might give them a call tomorrow

**bradf74** · 12-16-2015

I have the GMPP in my 68 Camaro. I ran the hot signal from the fusbaox through a relay to run both fans. I wired my fans to come on anytime the Ac compressor is on. fans also come on of caourse at 187 degrees on a signal from the ECU

**icemanrd19** · 12-16-2015

so the wire from the gmpp kit is a 12v not a ground?

**1989GTA** · 12-16-2015

With my E38 ECM it provides the ground(s) for the fan relay(s). I am sure yours does the same. You have to supply 12v to one side of the relay coil. The other side goes to the ECM output. I have no trouble with the idle rpm when the A/C is on. The ECM does not "know" when it is on as their is not feedback. It just automatically adjusts the idle.

**icemanrd19** · 12-16-2015

After looking at it plenty of times i know i can wire both of my fans to come on by the GMPP kit when at Temperature and run a AC override to run both fans when the AC is on. Only issue is i can not figure out a diagram to only allow the AC to override one fan instead of both of them. GMPP kit turns fans on and off not only by temperature but also by speed

Its either

1. Dual fans controlled by GMPP and AC
2. Drivers side Fan with gmpp and Passenger side fan with AC

I want Dual Fans by GMPP and Passenger side only AC override

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Controlling the fan with GMPP ECU