It should work. The way to verify what you have is to follow the trace from C2 17 (see "Step 2" in my original post above) on the motherboard. Most likely you have an unpopulated pad where there should be the 100k resistor. To the right of that, as shown in my post, is the 10k resistor that you would remove to replace with the 1.5nF capacitor.

Good luck!

 

well I can confirm that following your instructions adding the components did allow my 12602802 P59 to receive the a/c request and output the a/c clutch control. I changed my a/c selection in hptuners>system>ac to "analog cycling" and now i can monitor the a/c request and the a/c clutch engaged pid's with the scanner and the system works as it should (rpms, & fan). Ive wired my system basically as shown here with a high and low pressure switch (pins 17,43,& 55), keep in mind this is an L33 swapped into a 1998 Jeep cherokee.

 

So is this mod only for swaps using factory AC systems, or can you use it with a Vintage Air/Trinary switch?

Quite a bit of head scratching info out there, but I have the same IAC-less PCM and I’d like to use the computer to bump my idle when the AC comes on etc.

 

I used the factory truck compressor and the factory jeep evaporator and drier, added the biggest aftermarket condenser I could fit, and made custom lines that used the factory jeep high and low pressure switches plus an orfice tube. It's a Frankenstein system for sure! I don't see any reason why you couldn't tie your vintage system in with the pcm. I want to say I recall seeing some diagrams maybe on their website (not sure) for tying in the standalone system with the pcm. Using the components I used it was basically wired like the older truck systems were. I have my ac request(12+) run through my high pressure switch, a ground signal through my low pressure back to the pcm and the clutch output (ground) ran to my clutch relay. I see absolutely no reason why you couldn't make something work because once you set the pcm to analog cycling it just looks for the signals not pressures or anything. I haven't looked at trianary switches in a while but I believe it's high and low together in one switch and a fan output. I'm sure the controls send a signal for the compressor to run and the switch does all the work, I don't think their systems are very complicated, hell giving them a call may be all you need to do, they may have a tech person that could tell you exactly what you need to do.

 

I appreciate the quick reply! Unfortunately the tech guys seem to shy away from the AC using any PCM direction, basically saying the Trinary switch does everything it needs to do…both techs said I “just needed to bump up my idle”. Yeah, probably. But my LS has a cam in it, and I want to do this as right as I possibly can.
For the record my fans do come on correctly temp wise. No issues there. I don’t want to solder on my PCM board if this isn’t going to work with a trinary switch though. I DO think it will, I’ve just gotta find the correct wire diagram. Hopefully someone sees this thread and can point out one that’s worked with the aftermarket AC.

 

Which system are you using? Do they have any diagrams for it? We may be able to help you figure something out. I can see where they don't want to tell you how to modify it because If something happens engine, pcm, or ac system wise somebody may try to blame them.

 

I’m using a VA AC system, 2004 LQ9 with upgraded radiator and dual electric fans. Using 3 relay setup harness with Trinary switch. Blue Conn. Pin #42 : Low Speed cooling fan relay Control (Relay 1)

Green Conn. Pin #33: High speed cooling fan relay. (Relay 2/3)


Right now, it looks like the tune is set up for my original LQ9, so that will probably need to be redone as an Express Van or Corvette/GTO in order to use the 12v signal to bump the idle? Am I looking at this correctly?

 

man, i think the info i need to make my junk work is somewhere in here but i'm still confused. i know this is in the camaro forum but thanks to the magic of Google search, this thread has been the most informative and freshest so here goes:

my truck is an 01 Silverado with an LQ9/4l80 swap and a van P59 swap. factory 01 harness has been modified to work with the P59 and the truck runs and drives fine. still has the factory 01 fixed compressor and high/low switches. PCM is the 12589462 with IAC drivers so from what I've read, it is one that can work with the high/low pressure switches. i am using an Electric fan that is on a thermostatic switch and relays so it operates completely independent of the PCM and it works well, if i can keep from having to rewire the fans, i'd like to. I can command the compressor to engage via special functions, just need to know what i need to do to get it to do it by itself via the hvac controls. i have looked at the blue/green and the blue/red connector diagrams and pinouts, and i can see that there are cavities that are different between the two. is it something as simple as swapping the pins from one cavity to another (c2-17, 43 and 55 if my understanding is correct?)

my thought process is, the factory 01 was able to cycle the compressor via pressure switches since it was originally equipped with a clutch fan. i should be able to treat it as such and let the fans do what they already do. or am i completely off base here? hopefully someone can chime in and help me out because i've been reading for weeks and im still sweating in my truck. TIA

 

Is the A/C pressure sensor still required in this setup? The reason I ask is I modified my pcm as per this post, I'm now seeing the A/C request signal on my scan tool but the pcm will still not activate the compressor. I tried analog and analog cycling. C2-55 is grounded.
I'm running efans controlled by the pcm as well.

 

Analog is the only one that worked for me. I just tried unplugging the pressure sensor and the compressor stopped(it also won't go again once I plugged it back in), so it looks like you need to include it or look up a resistor that will fake a good signal.

 

Good to know, thank you. I previously read that a 80k resistor will fake 2V signal and is enough to trick the pcm. I'm going to see if I can find a pressure transducer that will fit onto my recirc switch.

 

I'm using a standard gm ac switch(from an '87) @ the drier into the AC request pin which takes care of the cycling. I did wire in a provision for a low pressure switch on the c2-55 gnd, but I haven't needed it(it's jumpered) The pressure switch i use for efan control only. AC started working again after a few key cycles once i plugged the pressure sensor back in. Best of luck.


*Edited correct function of c2-55.

 

That's basically how mine is wired. A/C request runs through the drier switch then into the high pressure switch behind the compressor(HT6) then to the PCM, while c2-55 is ran to ground.
What pressure sensor are you using and how is it plumbed in? I'm running a OBS truck setup.

 

I'm using GM 1551343 (same as donor, '04 sierra). Plumbed on the high side. I made all of my hoses with a kit from coldhose. The one fitting had an option. I should have put it inline instead for better hose routing.

 

If anyone is planning a similar project or needs to troubleshoot issues related to A/C request signals with different PCMs, your insight into the missing components and how to address them will certainly be beneficial. This kind of hands-on knowledge sharing is valuable for the automotive community and DIY enthusiasts. If you have any specific questions or need further assistance, please feel free to ask.

 

So I have a ls swap in a 280z and am integrating in a vintage air unit into the blue green ecu. Two things

1. I believe my ecu number is p12201111 so i popped it open and all the resistors and capacitors were already there (I'm super happy about that). So either I don't have the right ecu number or there are a few other ecu's that are not on the list of working units.

2. After reading through all the posts I'm a little confused on the wiring.

C2 17 - ac request 12v signal. This includes a high pressure switch.

c2 48 - ac clutch control. Ground signal for relay.

C2 55 - low pressure switch. Ecu provides 12v and is grounded through the switch??? Do I have to have this switch?

Right now my AC is stand alone with no issues other than my engine likes to stall at lights as I have a big cambicycle current wiring goes from my ac panel (request) to a high pressure switch then to the ac clutch where it is grounded. Assuming I don't need a low pressure switch I can just run my current wiring back to c2 17 and then add the pin to c2 48 for the clutch.

 

It sounds like you've got it right to me. Ground c2-55 if not using a switch. In my setup the high pressure switch cuts out on low pressure as well(gm style cycling switch from '87 K5).

 

Awsome, thanks for the quick response. I should be getting it wired up tomorrow.

I believe the vintage air pressure switch is also works as a high / low switch.

 

Just finished everything up and it works perfectly. Of note, I said in my post c2-43 and I should have said c2-48. But all in all everything works perfectly. This has been on my list of things to do for a while now.

 

Is there anyone who offers this service? And how much would it cost?