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I would like to see a single diagram of any GM or for that fact any manufacturer including the aftermarket systems that use a pressure sensor with a fixed compressor.
Check out the diagrams for a 2003 5.3l flex fuel suburban with the green/blue pcm. It runs a 10s20f denso compressor but has a pressure sensor on the high side and a low pressure switch . What a PITA in a swap.
aston, can you check what your a/c pressure is with your scanner? Looks like it has the capability to do that. What about A/C request status? can your scanner see that? Looks like it might be able to.
If you have the PCM programmed with an f-body tune I am 90% sure that it will kick up the idle without the a/c pressure sensor being connected, but it will not turn the fans on. I know that is how my green/blue PCM works.
The only way to check AC pressure is with the gauge setup that I used to fill the system.
When I filed the system I did it to Vintage Air's Specs.
The scanner may be able to check AC request on and I still have to check that.
It is an F-body tune, but as I stated the only connection between the AC and ECM is the AC Request wire that is 12 volts with the AC turned on (Compressor clutch engaged) and 0 volts with it off.
The only way to check AC pressure is with the gauge setup that I used to fill the system.
When I filed the system I did it to Vintage Air's Specs.
The scanner may be able to check AC request on and I still have to check that.
It is an F-body tune, but as I stated the only connection between the AC and ECM is the AC Request wire that is 12 volts with the AC turned on (Compressor clutch engaged) and 0 volts with it off.
But what tells the white wire to cycle on and off according to pressure from the binary switch?
The Vintage Air system cycles the compressor based on the Vintage Air switch. I have the white wire on the downstream side of the switch so when the compressor clutch loses 12 volts, the white wire loses it as well. Maybe I should .pdf and share the Vintage Air and PSI diagrams so everyone knows what I am talking about.
This is my last post as it seems to fall on deaf ears. If you use a fixed compressor you want to wire it like a Express van and set the compressor setting in the OS to be fixed. If you use a variable compressor you want to use the pressure sensor setup, wiring and PCM setting. Note you may need to turn off code P0530 to turn off the sensor code. Fixed compressors are made to cycle. This is done with the high pressure switch. There is a low pressure switch on the low side and a high pressure switch on the high side. The low is so you don't burn up the compressor with to low of a charge. The high keeps it from burning up or worse. You fans will come on when you wire this properly and you are using electric fans. Variable compressors are made not to cycle and run all the time. If you choose to use a fixed compressor setup with the sensor I would also run a low pressure switch. Why? The sensor is on the high side. Your compressor will burn up before the sensor turns it off at 30 psi on the high side.
Aston if you want to wire this properly you need to look at your wiring diagram and fit it to a Express van. The ac request should be 12 volts coming from your control panel to the pcm. Your binary switch will be on the output side of the pcm that should go to your compressor relay to turn the relay on. The rest is all vintage wiring. If you have more questions PM me I can help you with some diagrams, spreadsheets, etc.
69 Ghost , I am trying not to be deaf here, but I feel like we are talking different languages. Have you looked at my .pdf attachments? If I am reading you correctly you want me to disregard the wiring schematics given to me by Vintage Air and PSI and wire it like an Express Van. I will probably PM you, but I need to digest everything you are saying.
Aston, based on the diagrams I believe the white wire in the PSI harness goes to the red pcm connector pin 17. That tells the PCM that the A/C has been requested, however, it may not bump the idle up or the fans on as the f-body has feedback to red connector pin 18 when the A/C relay engages the clutch.
So the first thing I would try is putting 12V to pin 17 and pin 18 of the red connector. Hopefully that will get your idle up and fans working. My suspicion is that will bump the idle up but the fans still will not engage. If the red/blue PCM is like the newer green/blue pcm it will need to see A/C pressure via the sensor to engage the fans. You can confirm that by putting a jumper wire between blue pin 45 and red pin 14, that will max out the ac pressure that the pcm sees. Most likely the fans will run all the time with that jumper in place, but once we figure out the triggers for the fans we can work around the issues.
G-body, that is great stuff. thank you. I assumed PSI programmed the computer to work off of just that AC request signal, but I could be wrong. I will investigate further.
I opened up a dialogue with PSI and I should have done that from the beginning. I apologize if I wasted anyone's time here, but I want to finish up this post in case anyone else with my setup has a similar issue. I am going to copy and paste the discussion for everyone's reference.
PSI: The A/C request wire will stabilize the idle with the A/C on. It will not run the fans.
Me: How does it stabilize the idle?
PSI: The Pcm internally sees the 12 volts on that data bus and keeps the idle at the set target idle speed.
Me: Is that target idle speed supposed to be the same as with the AC off or can it be adjusted?
PSI: It can be adjusted for A/C, I would set it about 150-200 RPM higher than you're Regular idle speed.
Me: OK, my idle speed never changes and it actually stumbles when I first turn on the AC. It eventually smooths out but stays at the 800 RPM my tuner set the idle at. I will have to see if he will adjust that for me.
PSI: Sounds like you have a bigger cam. I would say if it smoothes out it is working, I would turn the idle up a little to compensate for the cam if it in fact does have a cam.
Me: Nothing too radical 223/231 at .050" and .610"/.617" lift.
Idle vacuum is 16" HG at 800 RPM
PSI: That size cam will affect idle parameters, the sudden drag from the comp.will affect the idle till the Pcm can compensate.
So bottom line is my cam is causing the idle to go unstable until the ECM can catch up and then all is well. Bumping up the idle speed with AC on should fix this. No wiring changes needed. I was wrong about the fans however, they will turn on and off in accordance with coolant temp as usual.
This is my last post as it seems to fall on deaf ears. If you use a fixed compressor you want to wire it like a Express van and set the compressor setting in the OS to be fixed. If you use a variable compressor you want to use the pressure sensor setup, wiring and PCM setting. Note you may need to turn off code P0530 to turn off the sensor code. Fixed compressors are made to cycle. This is done with the high pressure switch. There is a low pressure switch on the low side and a high pressure switch on the high side. The low is so you don't burn up the compressor with to low of a charge. The high keeps it from burning up or worse. You fans will come on when you wire this properly and you are using electric fans. Variable compressors are made not to cycle and run all the time. If you choose to use a fixed compressor setup with the sensor I would also run a low pressure switch. Why? The sensor is on the high side. Your compressor will burn up before the sensor turns it off at 30 psi on the high side.
Aston if you want to wire this properly you need to look at your wiring diagram and fit it to a Express van. The ac request should be 12 volts coming from your control panel to the pcm. Your binary switch will be on the output side of the pcm that should go to your compressor relay to turn the relay on. The rest is all vintage wiring. If you have more questions PM me I can help you with some diagrams, spreadsheets, etc.
The ECM with fbody/ybody calibration and pressure sensor replaces the trinary switch in a VA system. This should not be too hard to comprehend.
Aston. I would still try putting power to the pins I mentioned earlier. PSI may not have included the option to turn the fans on with the ac in their harness, but I would say it's fairly unlikely that they deleted that ability from the pcm.
Ok my problem seems so simple as I am using red blue 411 with all fbody parts 3 wire high pressure switch I have the wire diagram and feel like I am very close Here is my issue I'm using a stand alone harness so I'm running new wires from pcm to 3 wires on high pressure switch but my new pigtail has different colors and since I don't have any refferance I don't know where to wire the 5v supply and Inc ground and signal output from pcm This pigtail I have has 2 wires side by side one gray and one black and the other is blue I tried blue as supply and gray as signal and black as ground and also gray as supply and blue as ground I did just ground the black instead of splicing it to red 57 for now I'm just trying to get the ac to kick off and on for now Also here is another big question on the Fbody is the ac request a positive 12v request or Ground request to turn the ac on from toggle switch ??? Any advise at this point would be appreciated I have studied the fbody diagram 100 times Nowhere I can find shows this info Thanks Dan
Maybe someone with an fbody can take a picture of there high pressure switch like my picture of the switch to show how colors are on the plug there is a purple gray and red/black I just don't know how they would match to my new pigtail of blue ,gray , and black. Also if anyone knows the ac request signal circled in my picture in the previous post above is the pcm looking for a positive 12v signal or a ground to make the compressor engerize at red 17 on the pcm
Jonathon, the way you explained I have not tried just to verify at the way you explain The PIN numbers are right but the signal is not as the wiring show in diagram
Red 57 splices into aic
Blue 45 is 5v reference
Red 14 is pressure signal
I think you mention that #57 was reference 5v and I'm showing 57 is going to iac
Please take a look at my drawing I have drawn the pigtail plug showing it as I'm looking at it (pigtail Plug) Using my numbers I have drawn Where does a,b,c connect to 1,2,3
Thanks very much for your reply
Also notice my relay wiring and yes I do have red 18 and compressor going to 87 on my relay
Thanks again I have dash out this is the last thing to wrap up before the wires get tucked in
06-21-2016, 02:21 PM
