LS swap with ac wiring questions

Rodknok

Apprentice
Jun 14, 2022
86
33
I have a 84 GN that's getting a LS swap. I'm looking at the wiring for the ac system and wanted to know of any of the ac related wiring is in the efi harness. I started to pull the old efi harness out of the car and I'm not sure if I need any of the wiring from it. Thanks in advance
20220723_085123.jpg
 

Rodknok

Apprentice
Thread starter
Jun 14, 2022
86
33
Also I forgot to mention that my car has the electronic climate control.
20220724_120245.jpg
 

81cutlass

Comic Book Super Hero
Feb 16, 2009
4,227
113
Western MN
If you want to do it correctly yes.

The ac compressor should be controlled by the g body ac controls but you still communicate with the LS computer. The LS ECM controls idle bump and coolant fans that just using the g body control won't get you. However there's things in the g body harness you need like blower fan power, cycle switch and on signal you want to keep.

I put this video together since nobody seemed to describe how to do it.

Basically you give 12v to the compressor and tee off to the LS ECM to do the fans and idle if you don't want to go through the hassle of commanding the ECM and having the ECM go to a relay to trigger the ac clutch.

If your using a OEM variable displacement compressor you should use the entire LS ECM with the high and low side pressure switches but if you have an on/off style R4 pancake or sanden compressor this is the cleanest way to do it.
 
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Rodknok

Apprentice
Thread starter
Jun 14, 2022
86
33
If you want to do it correctly yes.

The ac compressor should be controlled by the g body ac controls but you still communicate with the LS computer. The LS ECM controls idle bump and coolant fans that just using the g body control won't get you. However there's things in the g body harness you need like blower fan power, cycle switch and on signal you want to keep.

I put this video together since nobody seemed to describe how to do it.

Basically you give 12v to the compressor and tee off to the LS ECM to do the fans and idle if you don't want to go through the hassle of commanding the ECM and having the ECM go to a relay to trigger the ac clutch.

If your using a OEM variable displacement compressor you should use the entire LS ECM with the high and low side pressure switches but if you have an on/off style R4 pancake or sanden compressor this is the cleanest way to do it.
 

Rodknok

Apprentice
Thread starter
Jun 14, 2022
86
33
If you want to do it correctly yes.

The ac compressor should be controlled by the g body ac controls but you still communicate with the LS computer. The LS ECM controls idle bump and coolant fans that just using the g body control won't get you. However there's things in the g body harness you need like blower fan power, cycle switch and on signal you want to keep.

I put this video together since nobody seemed to describe how to do it.

Basically you give 12v to the compressor and tee off to the LS ECM to do the fans and idle if you don't want to go through the hassle of commanding the ECM and having the ECM go to a relay to trigger the ac clutch.

If your using a OEM variable displacement compressor you should use the entire LS ECM with the high and low side pressure switches but if you have an on/off style R4 pancake or sanden compressor this is the cleanest way to do it.
You are the man! Thanks you so much
 

Zippymac

Not-quite-so-new-guy
Aug 18, 2021
42
18
Dripping Springs Tx
nice write up... I just used currentperformance stand alone harness and a sanden AC compressor with Hooker accessory brackets.
This harness: https://www.currentperformance.com/shop/stand-alone-fuserelay-module/
This site for the ECM Pin outs: https://lt1swap.com/
A kitchen table - ohm meter setting on volt meter several beers and alot of patience.
Made my own stand alone engine harness - the internal controls remounted to turn on the A/C and Fans and a signal wire to the ECM to increase RPMs when the A/C Switch has power.
I got a push mower throttle cable and fabricated the heater vent control cable out of that - it looks mostly factory anyway...
I got the project box from Amazon and the 2012 LaCrosse console on Ebay
 

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