Sleeper 71 lemans

Okay so I am reworking the harness for my ls swap and everything has gone very smoothly and I am nearly done but I have not figured out how the A/C compressor wiring is done. I want the pcm to control the A/C so it will kick up the idle and the fans.

I know I have to ground pin 55 to always have a low pressure sensor signal. Then there are the two plugs that plug into the A/C compressor. Plug 1 having the wire coming from pin 17 A/C request and a wire for AC high pressure cut out switch from the fuse block. Plug 2 has an AC compressor clutch solenoid feed from the fuse block and a ground wire.

What do I do from here forward? I’ve read lots of questions about how to wire blue/greens and ls1 wiring but not many people ask about red/blue trucks. Maybe it’s really simple and I just dont understand what actually powers the compressor.

gagliano7

On my 1999 truck harness i connected the the 12v from compressor to pin 17 and grounded pin 55 and mine works. I sent you a pm

Sleeper 71 lemans

Based on this wiring diagram ripped off of lt1swap, I don’t actually mess with wire that goes from pin 17 to the compressor. I just have a switch with 12v+ to the light blue wire that was on the same plug? And as long as the compressor doesn’t see high pressure then the cutout switch will connect the 12v+ to pin 17 kicking on the fans. Is this correct?

I still don’t know what to do the the other plug on the compressor

Sleeper 71 lemans

Or do I simply cut off the ac high pressure cutoff plug, tie the pin 17 ac request to the hvac control only, and let pin 43 power the compressor clutch?

1964SS

iTrader: (1)

Is the motor stock? normally you don't need to connect the pcm. The motor will see the load and adjust to get to its set idle speed automatically. For the fans I use a trinary switch so fans are constantly pressure controlled if ac is on.

B52bombardier1

Correct on the PCM not being needed for A/C idle control. My PCM adapts the idle speed very quickly to the change in load on the motor. I also run a relay assembly to kick on one of my two e-fans immediately once the compressor kicks on - Four Seasons part number 35879. This is required to control AC compressor head pressures because we can't wait for a fan to turn on at normal fan turn on temperatures and my system uses the standard sensors in the AC lines to prevent over and under pressure damage.


Rick

Shawn Robinson

Hi, I'm working on the same situation with a 99 truck ls swap in a 52 chevy with old vintage air. Were u able to figure out the ecm pin setup. I have the blue red ecm. And a single wire compressor. Needing to wire the compressor to work off pcm and shut off on wot. Ty for any info

gagliano7

On my truck the a/c idle control made a big difference. I am using the 1992 silverado compressor and when you first kick it on it will sometimes stall. I tried without hooking up the a/c idle control and it is much better hooking it up and it was very easy to do.