A/C compressor shut off using PCM?
09-10-2009, 08:56 AM
#1
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A/C compressor shut off using PCM? Can I use the PCM to shut off a aftermarket A/C compressor at WOT? I'm ordering my Vintage Air setup and looks like all the unit needs is a 12v source to shut off the compressor. Was wondering if the PCM worked that way originally.
I know I can install a switch on the throttle somewhere but if I can get the PCm to provide a signal that would be easier and cheaper.
I know I can install a switch on the throttle somewhere but if I can get the PCm to provide a signal that would be easier and cheaper.
09-10-2009, 09:19 AM
#2
Yes you can, but you'll need to use the factory pressure sensor, and then find the A/C request wires in your harness, provided you haven't removed them, and you'll have to wire it into a relay for the compressor clutch. It may not be easier or cheaper than adding a switch to the tb, but it will work better. You get the fans to come on with the air on and the idle to bump up also.
09-10-2009, 02:20 PM
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thanks for the info, guess I have some more research to do. The fans and idle bump would be nice. Wonder how the PCM knows when your at full throttle and shuts the AC comp off? Is it a injector duty cycle thing maybe?
09-10-2009, 05:49 PM
#4
The throttle position sensor tells it when it's at WOT. Also your sig says you have a 2000 Ls1, so the A/C request stuff will be there, should have told you that the newer truck PCM's, I think 2003 and up, don't have A/C request as it's run on a serial data line, I'm still trying to figure out how to make it work on my 6.0.
09-11-2009, 11:01 AM
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I did pull the pins from the harness, but everything is still in the build stage so putting them back in isn't an issue. Forgot about the TPS, haven't seen my car in 7 months so am stock piling parts now and just ordered my AC setup. Gonna grab the pin outs and look them up.
09-11-2009, 11:45 AM
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So what I have figured out so far is
A/C pressure sensor-
connect Blue-45 and Red 14, assume the 45 is a 5v signal to the switch, which closes and puts the 5v signal back to the PCm through 14, tellign the PCM, A/C is on. This should be installed on high side of refrig system.
Red 17, I can hook my dash control to this, when AC is on, dash switch will send a 12v signal to PCM telling it to send power to Red 43, and energizing the A/C clutch relay.
Red 18- A/C status signal, what is this?
Does that about do it, besides R-18?
A/C pressure sensor-
connect Blue-45 and Red 14, assume the 45 is a 5v signal to the switch, which closes and puts the 5v signal back to the PCm through 14, tellign the PCM, A/C is on. This should be installed on high side of refrig system.
Red 17, I can hook my dash control to this, when AC is on, dash switch will send a 12v signal to PCM telling it to send power to Red 43, and energizing the A/C clutch relay.
Red 18- A/C status signal, what is this?
Does that about do it, besides R-18?
Last edited by ssduane; 09-11-2009 at 11:54 AM.
09-11-2009, 01:06 PM
#7
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I don't have your pinout or ac wiring diagram in front of me, but the LS1 has a 3 wire high pressure trinary switch. AC Request from you VA control module to switch, AC Request out [if pressure is good] to PCM, PCM to AC relay. The third wire on the LS1 trinary switch is a 5 volt reference I belive.
Use the pinout with the AC compressor wiring diagram that is floating around here. I bought the LS1 trinary switch, brazeable ports for high pressure line, and a crimp in line if I couldn't get the brazing right before I figured out the LQ4 high pressure switch is different. Let me know if you are at all interested in any of these parts.
By the way, if you get the PCM to control the AC, I believe you have the option of what RPM to disable AC from within HPTuners.
Rob
Use the pinout with the AC compressor wiring diagram that is floating around here. I bought the LS1 trinary switch, brazeable ports for high pressure line, and a crimp in line if I couldn't get the brazing right before I figured out the LQ4 high pressure switch is different. Let me know if you are at all interested in any of these parts.
By the way, if you get the PCM to control the AC, I believe you have the option of what RPM to disable AC from within HPTuners.
Rob
Last edited by robbied31; 09-11-2009 at 01:10 PM. Reason: disabling AC
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09-11-2009, 01:28 PM
#8
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thanks for the info Rob, I'll see if I can find the AC schematic thats flaoting around. I ordered the Tri-switchand crimp in fitting from VA that goes inline, hopefully the fitting size is the same as the LS1 switch and will fit.
I would really like to get the PCM to disengage the clutch on full throttle and bump the idle too I have my fans hooked up via the PCM so that should work the way its intended.
I would really like to get the PCM to disengage the clutch on full throttle and bump the idle too I have my fans hooked up via the PCM so that should work the way its intended.
09-11-2009, 01:45 PM
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just found the schematic, think I got it figure out, just need to print out a bunch of pages so I can look at them instead of going from webpage to webpage.
03-11-2010, 09:25 PM
#10
The throttle position sensor tells it when it's at WOT. Also your sig says you have a 2000 Ls1, so the A/C request stuff will be there, should have told you that the newer truck PCM's, I think 2003 and up, don't have A/C request as it's run on a serial data line, I'm still trying to figure out how to make it work on my 6.0.
03-12-2010, 05:48 AM
#11
Would like to know this as well. Also, on a truck with an acummalator low pressure switch, should this be wired into the dash a/c request, which is a 12 volt positive signal, in "addition" to the F-Body trinary switch? thanx
Last edited by LS1GMCTruck; 03-12-2010 at 05:58 AM.
03-12-2010, 09:51 AM
#12
Well, I think I might have mine figured out, but not sure about an LS2. GA95DCMSS informed me that 2004 Express vans had DBW and also a regular A/C request, not the serial data A/C like the Silverado went to starting in 2003. It turns out that vans were like this until at least 2006 or 2007 according to the wiring diagrams on Alldata. I wired mine like the van, but have not been able to check it out to see if it works due to the fact that the VATS is still in the PCM. I was going to have the PCM programmed to a van operating system, but I haven't done it yet because when I hooked my scanner up to it, I can command the A/C on, and it comes on. However it doesn't come on when you put power to the A/C request wire. This is with both the high and low pressure switches jumped because the system isn't charged. I'm hoping that this is just because the PCM is not seeing any RPM, and when it starts it will come on. I'm going to hook a scanner to one of our service trucks at work tonight to see if the compressor comes on without the engine running, if it doesn't, then I think mine will work when the engine is running. I'll let you know what I find out tomorrow.
03-12-2010, 05:57 PM
#15
I think I would just wire it up like an F-body, with the three wire sensor, where all three wires go to the PCM, and not use the accumulator mounted switch. If the accumulator switch is a two wire switch (which I'm assuming is original to the 96 truck?) it's just an on/off switch, I can't remember right off if it's normally open or closed, but I can't see you really gaining anything by using it.
03-15-2010, 06:00 PM
#16
O.K., Thanks. Have never really got a straight answer on whether or not to use the accumalator switch in unisen with the F-Body trinary. But I guess that is all the computer needs, to operate the system properly. The A/C request(12 volt positive), coming out of the firewall from the dash on/off switch, is connected to A/C request wire coming out of the computer? Or does it connect to the positive trigger side of the A/C relay? I wouldn't think the computer should be fed a positive 12 volt signal of any kind, but I could be wrong. Again, Thanks
03-15-2010, 09:58 PM
#18
Well, I think I might have mine figured out, but not sure about an LS2. GA95DCMSS informed me that 2004 Express vans had DBW and also a regular A/C request, not the serial data A/C like the Silverado went to starting in 2003. It turns out that vans were like this until at least 2006 or 2007 according to the wiring diagrams on Alldata. I wired mine like the van, but have not been able to check it out to see if it works due to the fact that the VATS is still in the PCM. I was going to have the PCM programmed to a van operating system, but I haven't done it yet because when I hooked my scanner up to it, I can command the A/C on, and it comes on. However it doesn't come on when you put power to the A/C request wire. This is with both the high and low pressure switches jumped because the system isn't charged. I'm hoping that this is just because the PCM is not seeing any RPM, and when it starts it will come on. I'm going to hook a scanner to one of our service trucks at work tonight to see if the compressor comes on without the engine running, if it doesn't, then I think mine will work when the engine is running. I'll let you know what I find out tomorrow.