A/C Request Segment Swap

[RADustin]

While I'm under the truck searching for other issues, I'm going to wire up my vintage air to my a/c. Currently I use a corvette based COS5, 02020005 that was made from a corvette 12212156.

The corvette used a ground signal into red 17 for a/c request, and the camaro uses a 12v signal into red 17. I have the series II vintage air, so it is a simple compressor wire (12V) hooked to a thermostat.

I will add a relay in this compressor feed, that will use the thermostat side of the compressor wire as power and through current(85 and 30), use the a/c output on the ECM, red 43, as the ground(86), and hook the compressor side of the wire back to 87 to receive. I will also hook the status wire from the ECM, red 18, with post 87 on the relay for an accurate status. This will work well, but how to tell ECU I am ready for a/c?

I'd like to wire the thermostat side of the compressor wire (12v when vintage air wants compressor) to the a/c request pin. To do this I would need a camaro segment and maybe a different ecu. I don't have an 0411, I have something like a 09354896 I think as my ecu came from a 99 or early 2000.

Either way- end question is....what segment contains the a/c info that would allow a 12v request instead of a ground request? I assume it would be system, but I want to make sure. Not sure if I would have an ill effects by swapping this segment??


I did spell out everything I know so far for future searchers. I will post what works once I get there.

Thanks!

[RADustin]

the above idea has worked. I completed it last night. The ECU adds a slight delay into the vintage air comp request and idles up the engine as I ask it. No more stumble but I do have the idle set too high @1200. Going to bring it down to 850 and see if I like it. No ac I idle at 725.

Only issue- I don't have a techII with me right now and I can't verify the ECU actually knows the a/c is requested and on. It seems obvious it is- but I log state02 with the scan tool and the comp clutch relay never changes status. Not sure if there are other ways within the efilive scan tool to monitor the A/c request and status lines??

I did try to do RAFIG for the a/c on and it did not work- or didn't seem to work. Not sure what is going on there.

Last weird item I noticed was my cheap ebay engine harness had a green wire shoved in one of the a/c locations that I needed in the ECM plug. I unhooked it but I'm not sure how to confirm where it goes. The truck doesn't seem to have any ill-effects- so I am not sure. The truck harness originally didn't have provisions for ac or cruise- so I added myself. All the more reason to build your own harness.

[joecar]

You can use the EFILive scantool to log the appropriate STATExx pid to see AC Request (add a Status guage on Dash A).

[RADustin]

when I monitor the ac compressor relay it never goes active- but I know it is physically working and the truck runs 100000% better.

I have HPT in the mail- I can look at it with that. I think they have some extra PIDs for ac and what not more similar to a techII.

[turbo_bu]

just a thought - since you are using a slightly mis-matched set of OS / PCM, what kind of VIN # is programmed in there? Corvette, F-body, truck etc....??? I noticed that under the scan tool, it can matter as to which PID's get reported / updated based on what kind of VIN is programmed in the PCM. The programming I was playing with is under the scan tool programming of the VIN ... not just the VIN that is listed under the flash file.

[joecar]

when I monitor the ac compressor relay it never goes active- but I know it is physically working and the truck runs 100000% better.

I have HPT in the mail- I can look at it with that. I think they have some extra PIDs for ac and what not more similar to a techII.

The pid GM.STATE00 contains bit flags showing the AC Requested input and the AC Clutch Relay commanded output...

if AC Clutch Relay is never being commanded, check what is the state of AC Requested..