Vintage Air Wiring with LS Standalone Harness

[cebra]

My BP Automotive harness included a connector for "AC Pressure Sensor Wiring" which increases idle and turns the e-fans on when compressor is running (per the BP website). I have a trinary for my VA to turn on the fans so this isn't necessary but I would like to hook up the idle increase functionality if feasible. Can anyone aid me on how this may be done? Attached are the wiring instructions for the VA.

[ls1nova71]

What year is your engine?

[cebra]

It is a 2000 4.8L Tahoe engine. I am using the VA GenIV system if that matters as well

[ls1nova71]

A 2004 wont have a 12v A/C request wire, so in order to use that wire they included in the harness you would most likely need the factory GM pressure sensor. It would be easier to just run the VA as a stand alone unit, but tie the high fan relay (if you have both high and low) to the trinary switch so that it will turn the fans on when needed.

[MDPotter]

Originally Posted by ls1nova71

A 2004 wont have a 12v A/C request wire, so in order to use that wire they included in the harness you would most likely need the factory GM pressure sensor. It would be easier to just run the VA as a stand alone unit, but tie the high fan relay (if you have both high and low) to the trinary switch so that it will turn the fans on when needed.

Not to hijack this thread, but I will be doing the same thing in the future on my 2004 Gen III and my dad's 2012 Gen IV is a similar setup. On my dad's we installed (2) relays - one for each fan and also the trinary switch and we thought we had it installed correct. He took it to a local shop that has installed a lot of VA units to have the system charged and they added a third relay which turns on the second fan whenever the compressor is engaged. It appears that the wire coming from the VA compressor is the signal for this third relay. So is the trinary switch even doing anything in this scenario? Fan 2 cycles a lot as the compressor is constantly cycling (dependent on where the temp inside the cab is set). It seems to me that the trinary switch should control the fan, not the the compressor.

[cebra]

Originally Posted by ls1nova71

A 2004 wont have a 12v A/C request wire, so in order to use that wire they included in the harness you would most likely need the factory GM pressure sensor. It would be easier to just run the VA as a stand alone unit, but tie the high fan relay (if you have both high and low) to the trinary switch so that it will turn the fans on when needed.

Is this the same for a 2000 model? I am using the VA Sanden compressor so will just run it standalone and bump the idle tune up a bit if I can't easily get the idle to bump up when the compressor comes on.

[cebra]

Originally Posted by MDPotter

Not to hijack this thread, but I will be doing the same thing in the future on my 2004 Gen III and my dad's 2012 Gen IV is a similar setup. On my dad's we installed (2) relays - one for each fan and also the trinary switch and we thought we had it installed correct. He took it to a local shop that has installed a lot of VA units to have the system charged and they added a third relay which turns on the second fan whenever the compressor is engaged. It appears that the wire coming from the VA compressor is the signal for this third relay. So is the trinary switch even doing anything in this scenario? Fan 2 cycles a lot as the compressor is constantly cycling (dependent on where the temp inside the cab is set). It seems to me that the trinary switch should control the fan, not the the compressor.

Most people run 3 relays so both fans kick on in when the ECM goes to the high fan or when the trinary pressure triggers it. They may have hooked it up to run off the compressor rather than trinary but that would be more cycling than using a trinary which measures the pressure and turns the fan on at a certain pressure. You could have just run a binary if the e-fans are wired directly to the compressor.

[MDPotter]

Thanks for the info. I was just reading through another LSX Swaps thread posted today and eventually got to another thread with a lot of info on 3-relay wiring. I don't plan on buying my VA system for awhile after wiring everything, but I do want to go the 3-relay setup with my fans and I'm going to look at my dad's wiring closer to see what the shop did.