Another PCM controlled A/C question
Another PCM controlled A/C question Here goes: I'm using a Sanden 508 compressor, stock (69 Firebird) evaporator, 134a POA valve, 134a expansion valve, LS1 style High pressure sensor. Engine/harness/pcm is 2006 L59 Truck 5.3
C2 Pin 43 is the clutch engage (grounding circuit) circuit which I have routed to a relay to turn on power to a/c clutch.
How do I wire to turn a/c on/off on my original switch? Any additional signals other that the high pressure sensor needing to go to pcm?
Does the PCM automatically cycle the compressor on if the pressures are right?
C2 Pin 43 is the clutch engage (grounding circuit) circuit which I have routed to a relay to turn on power to a/c clutch.
How do I wire to turn a/c on/off on my original switch? Any additional signals other that the high pressure sensor needing to go to pcm?
Does the PCM automatically cycle the compressor on if the pressures are right?
Yep, this seems to be the case. From 2003 on up, the A/C is on a serial data line. Vans on the other hand still used an A/C request, but they are not DBW, so switching OS would work if you're planning on using a cable TB.
I'm keeping the DBW. Is there no other pin in the pcm that trigger c2 pin 43 to ground?
Can I keep the high pressure sensor going to the pcm...will it still control the fans?
Bottom line is that I don't want the compressor to be running constantly. Will the low pressure switch cycle it?
I'm clueless to the a/c system...just know that I don't want the compressor to constantly run.
Can I keep the high pressure sensor going to the pcm...will it still control the fans?
Bottom line is that I don't want the compressor to be running constantly. Will the low pressure switch cycle it?
I'm clueless to the a/c system...just know that I don't want the compressor to constantly run.
Launching!
Joined: Jul 2004
Posts: 223
Likes: 0
From: Potomac, MD
Not sure how your truck PCM handles AC. If it has a pin for AC request then you can probably run AC through PCM, like the earlier LS1 PCM's.
If not then you will not, as far as I know, be able to have the PCM control the AC and you will wire it directly using the controls of the AC system and pressure switches.
If not then you will not, as far as I know, be able to have the PCM control the AC and you will wire it directly using the controls of the AC system and pressure switches.
Why does the compressor running constantly bother you? If you're running the factory A/C with a POA valve, that's the way it was designed to operate. The compressor didn't cycle. There are replacements for the POA that basically do away with it, and they have a pressure switch that will cycle the compressor.
I have an updated POA valve for use with 134. It has a low pressure switch. Will that switch (hooked to the ground side)cause the compressor to cycle?
The "new" POA valve seems to be nothing more than a piece of pipe with threads on the ends, two small port for evap/stv valve, and the pressure switch.
The "new" POA valve seems to be nothing more than a piece of pipe with threads on the ends, two small port for evap/stv valve, and the pressure switch.
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That's not a POA valve, that's the part I was refering to that takes the place of the POA valve. That does make the compressor cycle. It makes the A/C system rely on the expansion valve. But as for your original question, controlling it with the PCM, I'm still not sure it can be done with the later truck PCM. I've personally been running mine completely seperate of the PCM, using a trinary switch to turn the fan on, without any real problem. It does SLIGHTLY bog the engine down for a split second when the compressor kicks on, but it's not really noticeable.
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Teching In
Joined: Mar 2008
Posts: 10
Likes: 0
From: germany
AC request I was in the same situation. I have a 2007 5,3 LMG with E38 in my 1997 Tahoe. The AC request is all CAN. The AC switch on the AC controlmodul is the driver input, the AC Control modul puts the AC request on the CAN bus.
I did the following: I wired the 1997 AC switch signal through a 12V relais to have GND when AC is switched on. This signal is wired through my 1997 cycling switch in the reciever/ drier to the 2007 systems AC Clutch relais in the 2007 engine fuse box. So then we have a cycling compressor but without the ECM controlling idle when the AC is on. The ECM actually doesn't know that the AC is running.
Now the interesting part. : Although the ECM doesn't know about the backdoor I use to switch on the AC, it reacts on the 2007 pressure switch in the high pressure hose and switches the fan speed according the AC system pressure.
For my own peace of mind I switch on the fans on the low setting everytime I switch on the AC.
I read your are in Germany, if you find the time, just come by and we can sort out the AC stuff. I am located between Frankfurt and Würzburg.. just drop me a line..
You are very welcome..
Harald
here are some pics of my swap:
http://s301.photobucket.com/albums/n...bum/?start=all
I did the following: I wired the 1997 AC switch signal through a 12V relais to have GND when AC is switched on. This signal is wired through my 1997 cycling switch in the reciever/ drier to the 2007 systems AC Clutch relais in the 2007 engine fuse box. So then we have a cycling compressor but without the ECM controlling idle when the AC is on. The ECM actually doesn't know that the AC is running.
Now the interesting part. : Although the ECM doesn't know about the backdoor I use to switch on the AC, it reacts on the 2007 pressure switch in the high pressure hose and switches the fan speed according the AC system pressure.
For my own peace of mind I switch on the fans on the low setting everytime I switch on the AC.
I read your are in Germany, if you find the time, just come by and we can sort out the AC stuff. I am located between Frankfurt and Würzburg.. just drop me a line..
You are very welcome..
Harald
here are some pics of my swap:
http://s301.photobucket.com/albums/n...bum/?start=all
Launching!
Joined: Jul 2004
Posts: 223
Likes: 0
From: Potomac, MD
Sounds like you would need the gm engineer for that one. Interesting though.
Most run their AC without the pcm and they work fine. The nice thing about the pcm control is it kicks up idle before clutch engages.
I think the only way to do it is to use an older pcm, until someone figures out how to use serial data.
Most run their AC without the pcm and they work fine. The nice thing about the pcm control is it kicks up idle before clutch engages.
I think the only way to do it is to use an older pcm, until someone figures out how to use serial data.
Teching In
Joined: Mar 2008
Posts: 10
Likes: 0
From: germany
serial data one easy way is to take an AC control modul from the same year/system as the ECM. It could be installed in a hidden place under the dash. Then trigger the control modul's AC request input with a "normal" on/off AC switch and the modul does the AC request on the CAN bus.
That's the way I will do it very soon.
Harald
That's the way I will do it very soon.
Harald
Launching!
Joined: Jul 2004
Posts: 223
Likes: 0
From: Potomac, MD
Harald please let us know when you have done this as I'm sure many will be interested.
How do you get the AC module to send the serial data to the PCM. You mentioned just using your AC request signal from your regular switch(12v). Is there a way to get around the logic in the module as it uses a bunch of parameters before deciding what to do I think.
Do you know if the serial data signal is the same across GM for AC?
Interesting.
Thanks for your R&D on this.
How do you get the AC module to send the serial data to the PCM. You mentioned just using your AC request signal from your regular switch(12v). Is there a way to get around the logic in the module as it uses a bunch of parameters before deciding what to do I think.
Do you know if the serial data signal is the same across GM for AC?
Interesting.
Thanks for your R&D on this.
