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That's the way the F car system works and Greg and I were at one time trying to perfect this hot wire job. Maybe he'll chime in. I forgot where we were with his (he runs the 2002 Camaro PCM that works more like what you're talking about).
As far as the 2004 PCM, it's not voltage but an actual Class2 message from the HVAC to the PCM requesting AC meaning you'll have to use the 2004 AC control to make it work like stock.
Ohhh...I gotcha...well, I guess I'll get to digging around some more and reading the GM Service Info on the AC to see if there is someway to make it happen.
Thanks again for the input!
Cody B.
I haven't got around to doing mine yet, been way busy with other distractions and just being lazy on other day vegging out on here. I'll post up when I get some real results.
Yea, I hear you on the way too busy part. Been working on finishing up a 5.3 into an 1981 Jeep CJ...we should start it up tomorrow and then its back to my car...
But given its close to winter coming up, I figure I'll let the minor AC nuances slide till oh...next June :)
THanks for the help though guys,
Cody B.
I'll have to dig, but the 2004 controller can take a discreet input instead of a class II message. Talk to some of the better tuners out there, they may know how set it up. It most likely needs a pin to the PCM that is not in the regular diagrams.
Look through the service info for a 2003-2004 Van vs. a Sierra. They use the same controller, same software, but depending on which pin you use, and likely some different cal values...
This is the Sierra.. on the blue connector
Pin Wire Color Circuit No. Function
14 RED/BLK 380 A/C Refrigerant Pressure Sensor Signal (A/C)
43 DK GRN/ WHT 459 A/C Compressor Clutch Relay Control (A/C)
80 BLK 2751 Low Reference (A/C)
On the savana, blue connector.
17 DK GRN/WHT 2523 A/C Request Signal (C60)
43 DK GRN/WHT 459 A/C Compressor Clutch Relay Control (C60)
55 DK GRN 603 A/C Low Pressure Switch Signal (C60)
If you poke through the service manuals, and look at the schematics.. I think you'll figure out a solution. I'll bet one is ClassII (Sierra), one is a hardwired (aka discrete) input on the van..
Did you ever figure this out? My engine and PCM is an 06. I have the A/C hooked up and working in my 85 on just the truck's controls, and it works fine. But if I could figure out how to tie it into the PCM I probably would.
There isn't a way to do it currently on the 03+ PCMs. I have been after HPtuners to look into a way to switch the AC signal from Serial to switched, but no dice yet.
Red, did you ever figure out how to do it on yours?
Nope, was running a Sanden compressor so I just triggered it from the 93 signal wire to the clutch and it stayed on all the time, no cycling. The coils would freeze up from time to time and I'd have to turn the a/c off so the fan could thaw it out.
Well that sucks. Seems like if it was engaged all the time it would put a load on the motor all the time?