I was told the A/C request on the 03+ computers is a serial data signal from HVAC control module, no wire input to trigger ac.

What exactly does this mean?I want ac.

I'm not an expert as to why A/C can't be controlled by a 58x ECM swap. Speartech doesn't offer it on their 58x harnesses, and they recommend vintage air. I kept the original 1984 design on my Trans Am. I added a vintage air trinary switch to replace the high pressure switch. The old style compressor had a high pressure switch. The sanden compressors do not.

Need more info from you than just that you want A/C.

CANBUS (Serial Data) is used to integrate PIM, BCM, and ECM control functions.

What Johnw999 is describing, is a work-around which allows operation of A/C but is not ECM controlled. This could result in stall conditions at stop light, and has no high rpm cut-off protection. As long as you have a good memory and keep the operating conditions in mind, you can have functioning A/C this way. You could program a higher idle rpm to avoid stall, and remember not to high rev with A/C on (we all have excellent right foot control, here ).
Trinary switch monitors psi and will cut-off compressor according to high and low presets.

58x?Relucter?Mine should be 24 as its a gen 3.

But sweet to know a work around.

https://www.thirdgen.org/forums/ltx-...reen-blue.html

This is everything you need to get ac working with the stock hvac controls, high pressure switch, and ecm.