A/C ecm wiring for idle

[Justin71105]

Originally Posted by A1971Blazer

Good info, thanks!

My PCM is mounted on the back of the core support, so there's easy (relatively) access to it. I could easily add the wires and pick up the 12v signal at the compressor connector, ground would be simple as well.

Mine is a DBC (red/blue) but I suppose the PCM would be looking at the same i/o for a signal, and the IAC would make the adjustments to the idle.

I will need to look at my harness to see what wires may be there, and the PCM pinouts that correspond to the AC signal.
I'll hook up the scanner and check some readings first.
Attachment 2425299

From my reading on this the red/blue all have the needed circuitry inside the ecm.

Green/blue like mine only a certain set of them have the needed circuits inside the ecm, lt1swap has a list of them and mine matched.

They also have the step by step to add the needed chips inside blue/green ecm missing the circuitry to make it work but I was happy I did not have to go through all that.

For my compressor SD709 (04709-VMA) from VA I have AC set to Analog cycling (fixed compressor) in tune and it would need to be set to Analog for a variable compressor.

[Justin71105]

Make sure pin 55 has a good ground, had a few times the past few days where it would stumble and I would see on the scanner that AC Active and AC clutch enabled would turn off with AC request still on.

I have a stud on firewall I am using as a ground for my engine harness and put that ring connector on it from pin 55 on ecm. Found when I tightened the connector it got pulled into the washer I have against the firewall and wasn't making great connection.


The wire is fairly small 22ga and the ring connector is a 5/16- 16ga I have a bunch of. Solved this problem today, I made a new wire to go between ecm and that ground, crimped the connector on for ecm and soldered as well, did the same for the ring terminal. Used a smaller inner diameter washer for firewall so it wouldnt get pulled into the hole when I tightened. May order some 1/4 - 22 ga ring terminals if it becomes an issue later on. But after soldering it in I think it will be fine.

Ran VCM scanner and did not lose those two values at all while I had the AC request.

I also adjusted the Base running airflow in gear up 0.8 g/s for my normal running temp and this looks to have taken care of the stumble in reverse with a/c on and off.

Will take it out later and make sure but it did even just pulling up driveway and backing down I had no issues like I did earlier this week.

The loss of ground (closed) signal to ecm caused it to turn off ac clutch and deactivate ac like it was low on freon.

This also caused the ecm to drop the idle assist I get even though the AC request was still active since that is a standalone 12v wire from VA wiring.