A/C Compressor activation on P59

They go by many names, P01, P59, VPW, '0411 etc . Circa 1999 to 2006. All VPW OBD2 PCMs.
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A/C Compressor activation on P59

Postby PeterTremonti » Tue Jul 28, 2020 1:35 am

I've been looking up how to turn on the A/C with the PCM in a swap I just did on my 76 GMC Sierra Grande and found out that the 2003 and up PCMs are all activated via Serial 2 Data from the HVAC module. Is there any way that tell the PCM that the A/C needs to be on (to turn on the fan/raise the idle/turn on the compressor) without having an HVAC module? On the P01s there is just a 12V signal to tell the PCM that the A/C activation is requested.

PCM info:

P59 1mb
HDW 12583660 - SERV 12586242 - OS 12587603 - 2004 Tahoe program data pull
programmed into a 2003 Suburban with the following numbers:

HDW 12580786 - SERV 12582605 - OS 12579405

I swapped the OS because the XDF was readily available for the 2004 operating system. Everything seems to be running fine at the moment except for a few sensor faults (rear O2s and knock sensors) which are likely bad based on the vehicle I pulled it from.

Any ideas or should I just make it a dumb A/C system run off of the 76 wiring and just let the PCM figure out the idle on its own and be unhappy with me possibly?

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Re: A/C Compressor activation on P59

Postby bubba2533 » Tue Jul 28, 2020 3:03 am

What OS are you running? You list two different ones, so not sure what one you are using. I think 12587603 would be the better of the two of those since it has an XDF. The XDF I have has the A/C type defined, but I am not sure what the values are.

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Re: A/C Compressor activation on P59

Postby Gampy » Tue Jul 28, 2020 3:49 am

If I understand correctly, you are using HDW:12580786 and programed it with a bin from HDW 12583660 - SERV 12586242 - OS 12587603 - 2004 Tahoe program data pull. ??

Os is good, however, both HWID's are non IAC, I believe you need a IAC unit, IAC units have analog A/C. (Hopefully a tuner will correct me if I'm wrong)
Meaning one of the following HWID's (noninclusive),
12570558
12575502
12583659
12589161
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Re: A/C Compressor activation on P59

Postby PeterTremonti » Tue Jul 28, 2020 6:00 am

Gampy wrote:If I understand correctly, you are using HDW:12580786 and programed it with a bin from HDW 12583660 - SERV 12586242 - OS 12587603 - 2004 Tahoe program data pull. ??

Os is good, however, both HWID's are non IAC, I believe you need a IAC unit, IAC units have analog A/C. (Hopefully a tuner will correct me if I'm wrong)
Meaning one of the following HWID's (noninclusive),
12570558
12575502
12583659
12589161



This is correct. I'm using the 2003 Suburban hardware with a flash and OS from the 2004 Tahoe. I have DBW currently so I can use my cruise control without additional hardware. Not sure if that was necessary but it's what came with my parts car. I'm going to hope there's some way of running A/C with a DBW throttle and no HVAC module in between since I've already tossed it with the parts vehicle.

Additional note. Both vehicles were 5.3L L59 Flex fuel 2wd which is why I was assuming it wouldn't be a problem and haven't seemed to have any so far. I'm just working on getting the A/C to work in my head while I have the hard lines made up.

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Re: A/C Compressor activation on P59

Postby ironduke » Tue Jul 28, 2020 12:23 pm

So I see 2 ways of doing it...

Work out the serial message from BCM to ECM and build a little box that sends the a/c request message.. I don't know if this will work with a missing hvac control? Do they do a handshake when started? or does it just send the message when the a/c is turned on and repeat it probably every 3 seconds or so?? I'm buried right now but I could possibly sniff the messages on my 03 truck looking for the message, little trial and error with an elm327 and you could find out if this is viable..

Or change the calibration/Os to a different type of ac control.. I don't have yours but I took a look at a stock 04 bin.. Looks like that one is set up for serial cycling..
I have not done any work or towards this but on the file I looked at 0x1f842 is the byte for a/c type.. I don't know if changing this and using the old pin for analog cycling would work, or if passive would help the ecm deal with a/c load all by itself?

You'd need to adjust the checksum but
0x00 serial
0x01 serial cycling
0x02 analog
0x03 analog cycling
0x04 passive
0x05 not equipped

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Re: A/C Compressor activation on P59

Postby PeterTremonti » Wed Jul 29, 2020 2:03 am

ironduke wrote:So I see 2 ways of doing it...

Work out the serial message from BCM to ECM and build a little box that sends the a/c request message.. I don't know if this will work with a missing hvac control? Do they do a handshake when started? or does it just send the message when the a/c is turned on and repeat it probably every 3 seconds or so?? I'm buried right now but I could possibly sniff the messages on my 03 truck looking for the message, little trial and error with an elm327 and you could find out if this is viable..

Or change the calibration/Os to a different type of ac control.. I don't have yours but I took a look at a stock 04 bin.. Looks like that one is set up for serial cycling..
I have not done any work or towards this but on the file I looked at 0x1f842 is the byte for a/c type.. I don't know if changing this and using the old pin for analog cycling would work, or if passive would help the ecm deal with a/c load all by itself?

You'd need to adjust the checksum but
0x00 serial
0x01 serial cycling
0x02 analog
0x03 analog cycling
0x04 passive
0x05 not equipped



All that is interesting and I really wish I got into computer programming when I left highschool like I planned. Instead I got into auto repair and don't know as much about this stuff as I'd like. I'm a bit jealous of how much info everybody here is able to provide because I love knowing how things work and why they do what they do. That being said, I don't know how to sniff messages from my OBD port and I'm sure I wouldn't understand what they mean at this point without learning a bunch more on the topic.

What I do know is that everything I've read said 2003 and up (I'm assuming the P59 switch from the P01) uses serial data to turn on the A/C. I know the vans have always been behind on technology and that might be worth looking into but I also haven't been able to check much into it right now. I'd love to go into my bin and change some bits/bytes around but I don't know how to do that at the moment and all I have to play with is TunerPro for adjusting variables in the bin. Speaking of which, I'll attach the bin I've uploaded into the PCM I'm using below. I'm curious about the difference between "analog" and "analog cycling" that you've described above along with the "passive" labels.
Attachments
HDW 12583660 - SERV 12586242 - OS 12587603 - 2004TahoeDBW5.3FlexFuel VATS Deleted by PT.bin
(1 MiB) Downloaded 53 times

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Re: A/C Compressor activation on P59

Postby ironduke » Wed Jul 29, 2020 5:09 am

So.. 2003 2wd silverado has a/c control over data line.. 2003 Express van has a/c controlled with a switch going thru the high pressure switch and another signal from the low pressure cycling switch goes to the ecm.. might this be analog switching??
Might be able to just find an express van bin file and work from that.. Below is just the schematic from the express van for the a/c control..

If you wanted to modify yours I think you could just modify the bin as needed with the info I've given and then load it into tuner pro to let that correct the checksums for you..

2003.express.van.compressor.controls.pdf
(195.18 KiB) Downloaded 57 times


edited to add that 2004 express van wiring is the same for compressor controls..

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Re: A/C Compressor activation on P59

Postby PeterTremonti » Wed Jul 29, 2020 6:02 am

ironduke wrote:So.. 2003 2wd silverado has a/c control over data line.. 2003 Express van has a/c controlled with a switch going thru the high pressure switch and another signal from the low pressure cycling switch goes to the ecm.. might this be analog switching??
Might be able to just find an express van bin file and work from that.. Below is just the schematic from the express van for the a/c control..

If you wanted to modify yours I think you could just modify the bin as needed with the info I've given and then load it into tuner pro to let that correct the checksums for you..

2003.express.van.compressor.controls.pdf


edited to add that 2004 express van wiring is the same for compressor controls..



I looked at the diagram and checked the pins for the van vs the pins for the suburban via http://lt1swap.com/2004vortec_pcm.htm and those pins are not used for the 2003 Suburban harness. I wonder if the hardware is capable of running it that way internally. When I get my hoses made up I will try it this way. In the mean time, I'll be looking for a tune for an express van with a flex fuel 5.3.

I wonder if just changing the vehicle value in the bin file will make it think it's in a van without changing anything else and just have the compressor work out. I'll try some things and see when it's possible. Thanks for the diagram Duke!

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Re: A/C Compressor activation on P59

Postby ironduke » Wed Jul 29, 2020 6:21 am

Here's your file converted to analog switching..

If I had to guess the difference between analog and analog switching.. Might just be some systems have a low pressure cycling switch and a fixed orifice system named CCOT systems(Cycling Clutch Orifice system), others have a thermal expansion valve(TXV) that is supposed to change as needed and NOT cycle the clutch repeatedly.. Yours would be a CCOT system..

Not sure I'm right, just my best guess.. I am often wrong btw, lol..


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Re: A/C Compressor activation on P59

Postby PeterTremonti » Wed Jul 29, 2020 6:43 am

ironduke wrote:Here's your file converted to analog switching..

If I had to guess the difference between analog and analog switching.. Might just be some systems have a low pressure cycling switch and a fixed orifice system named CCOT systems(Cycling Clutch Orifice system), others have a thermal expansion valve(TXV) that is supposed to change as needed and NOT cycle the clutch repeatedly.. Yours would be a CCOT system..

Not sure I'm right, just my best guess.. I am often wrong btw, lol..

HDW 12583660 - SERV 12586242 - OS 12587603 - 2004TahoeDBW5.3FlexFuel VATS Deleted by PT (1).AC.Analog.cycling.bin


Awesome! I'm going to save this for later. Just thought about the a/c compressor. I'm going to have to see if the vans use the same compressor as the trucks just to be sure there's no difference.

I do have an orifice tube per the parts guy at Advance Auto (they're always right the first time right?) but I remember seeing something with a sensing tube coming out of a brick near my evaporator. I'll have to look at it when I get home. It's too hot out to drive with no A/C.

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