Trinary switch ls3 Fan on with a/c
 

Hello, I have a crate ls3 engine. I am hooking up a trinary switch and want the fan to come on when the A/C turns on. My relay is from VA and it has 5 wires. 1 full time power, 1 ignition power, 1 fan wire and 2 white wires. My question is do I hook up all the wires as in the diagram and ground both white wires and leave the blue wire on the trinary switch unhooked?

Also my rpm is dropping and sometimes shutting engine off when the a/c is turned on. Do I need to get the engine tuned?

I'm almost at this same stage. Would love to know what steps are needed.

I think this diagram is pretty clear. You want the second drawing with the trinary switch. If you ground the white wires the fan will always be on.

http://www.vintageair.com/Instructions2013/900471.pdf

You are going to need to use the second white wire to allow your ECM to turn on the fan.

You only have one fan? Most setups I have seen have two fans.

Don

what harness are you using?

I was wondering same thing. Doesn't your LS harness already have a fan relay? If it does I am not sure that the VA relay is needed. Just use the trinary switch to activate the LS harness relay, assuming the ECM pulls the fan relay coil to ground.

Or if you are stuck on using the VA relay just use the ECM and VA relays to power the fan in parallel.

Don

The LS fan relay will not turn on the fan when the a/c commands it too. It only commands it to turn on when the engine temperature reaches its limit.

I am using the vintage air wiring relay harness. I originally tried attaching one of the white wires to the ecm to control the fans and the rest of the wires exactly as the diagram showed. that didn't work. I have the same diagram that was posted above. I tried powering the relay harness with full time power on one wire and instead of the ignition power wire, I attached it to "a/c power on wire" and then grounded the white wires. this allowed the fan to come on everytime the a/c turned on but the car would low idle until it shut down and it left the blue wire on trinary switch unattached. Also I am running twin fans, thinking I would run 1 fan for the a/c and the other fan connected to the ecm.

Your plan is not a very good one. You will most likely need both fans under ECM control at times.

I recommend you buy the two speed Entropy fan controller which has an AC input. It works great and everything is programmable if you don't want the defaults. Two speeds will also help keep it a little quieter.

http://www.entropyrad.com/lsx-series...SABEgL3yvD_BwE

Not sure about your idle issue but I suggest you sort out this fan wiring first and see if it goes away. It almost sounds like you are overloading one of the signals with your wiring errors.

If you choose to ignore this advice you will likely find that you need to use the control line to the ECM fan relay and not the fan power line from the relay to connect to the white wire on the VA relay. The white wire is looking for a ground, not 12 volts to turn on the fan.

If you want more specific advice take the time to post up a complete wiring diagram of what you connected.

Don

I believe you have to add a wire, sensor and adjust the setting in your pcm for it to function like that. There is some good information in this thread, long but troves of information. Maybe John Parsons (ParsonsJ) can add something to this. I remember reading a while back that he added it to a customer's car.

https://lateral-g.net/forums/show...t=John+pwm+fan

Are you running a GMPP harness? The GMPP setup only has one fan output. I bought a kit from PCMofNc that adds another relay/output to the GMPP relay center. I never used it and ended up using the Entropy system. If you are interested in that thing let me know.

I also have the same issue with the idle rpm drop with AC on. Will be watching this thread.

I have an LS3 connect and cruise in my wife's 69 with vintage Air and the Entropy controller. It does not stall when the AC compressor kicks on. Runs fine.

I am not following what PWM fan control has to do with the OP's questions.

Don