GMPP Stage 3 with A/C
09-16-2007, 01:32 AM
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GMPP Stage 3 with A/C
This is a somewhat long post with three large images but I felt that the subject material should be shared with my fellow Cobalt owners. ......GMPP Stage 3 with N2O at https://www.cobaltss.net/forums/show...66#post1481166
I wanted Stage 3 but being a 63 year old semi-retired ASE and GM master technician, wanted A/C also. The factory PCM controls the A/C compressor clutch operation by grounding the A/C compressor clutch relay to apply power to the A/C compressor clutch resulting in the A/C compressor running. The PCM monitors various functions when making the decision on whether to ground the A/C compressor clutch relay or not. This function as we know is disabled in the GMPP Stage 3 PCM.
I am not responsible for anything you do to your vehicle. The following modification works for me on my 06 SS/SC. Verify PCM pin numbers and circuits on your vehicle.
I provided an external ground for the A/C compressor clutch relay via a toggle switch. I solder spliced a wire (amber in image) into the PCM C1 pin 6 wire and ran it to my toggle switch located in the passenger compartment. The other leg of the toggle switch connects to ground. This provides me with the ability to turn the A/C compressor clutch on and off by grounding the A/C compressor clutch relay when I turn the toggle switch to the "On" position.
Okay, I now have A/C but since I turned the A/C on with my toggle switch the PCM can't turn it off if the refrigerant pressure gets low as it does with PCM controlled A/C. One of the parameters the PCM monitors is A/C refrigerant pressure in order to prevent compressor damage if the system is low on refrigerant. If the A/C system were to develop a leak and get low on refrigerant and the compressor were to continue to run the compressor would be damaged in short order due to the lack of lubricant.
I provided a refrigerant pressure signal to my Interceptor analog 1 input that monitors my A/C refrigerant pressure sensor signal voltage. I then set my Interceptor Annunciator warning lights to come on if my refrigerant pressure sensor signal voltage drops below 1.0 Volts, which will provide me with a visible warning that my A/C system is low on refrigerant whereby I can turn off the toggle switch to prevent damage to the compressor. I provided this A/C pressure sensor signal voltage by solder splicing a wire (white in image) into PCM C1 pin 26 wire and connecting the other end of the wire to my Interceptor analog 1 wire.
The Annunciator only accepts whole number settings and 1.0 volts happens to be about the static A/C pressure on my system. So, the Annunciator warning lights may come on when there is no real problem but it gives me a visual indicator and a reminder to check the analog 1 voltage to determine if A/C pressure signal voltage is too low so that I can turn off the A/C compressor.
Okay, I now can turn my A/C on and off with my toggle switch and I have provided a visual indicator to warn me if my A/C system is low on refrigerant. I have verified on my 06 SS/SC that GM did not alter the PCM’s ability to control the cooling fans based on A/C refrigerant pressure signal. I never turn my HVAC blower to the “Off” position (it is usually on low or #1 setting) thereby making sure that I always have airflow across the evaporator in case I have turned the A/C on with the toggle switch.
The beauty of the above modifications is that when I run my OEM Stage 2 PCM, I turn the toggle switch to the “Off” position and restore full PCM control of the A/C compressor clutch relay.
My Nitrous install will follow in another post.
Amber and White wires solder spliced into PCM circuits
.jpg)
PCM C1 terminal pin identification
View of PCM and wiring after modifiacation showing no visible modification
I wanted Stage 3 but being a 63 year old semi-retired ASE and GM master technician, wanted A/C also. The factory PCM controls the A/C compressor clutch operation by grounding the A/C compressor clutch relay to apply power to the A/C compressor clutch resulting in the A/C compressor running. The PCM monitors various functions when making the decision on whether to ground the A/C compressor clutch relay or not. This function as we know is disabled in the GMPP Stage 3 PCM.
I am not responsible for anything you do to your vehicle. The following modification works for me on my 06 SS/SC. Verify PCM pin numbers and circuits on your vehicle.
I provided an external ground for the A/C compressor clutch relay via a toggle switch. I solder spliced a wire (amber in image) into the PCM C1 pin 6 wire and ran it to my toggle switch located in the passenger compartment. The other leg of the toggle switch connects to ground. This provides me with the ability to turn the A/C compressor clutch on and off by grounding the A/C compressor clutch relay when I turn the toggle switch to the "On" position.
Okay, I now have A/C but since I turned the A/C on with my toggle switch the PCM can't turn it off if the refrigerant pressure gets low as it does with PCM controlled A/C. One of the parameters the PCM monitors is A/C refrigerant pressure in order to prevent compressor damage if the system is low on refrigerant. If the A/C system were to develop a leak and get low on refrigerant and the compressor were to continue to run the compressor would be damaged in short order due to the lack of lubricant.
I provided a refrigerant pressure signal to my Interceptor analog 1 input that monitors my A/C refrigerant pressure sensor signal voltage. I then set my Interceptor Annunciator warning lights to come on if my refrigerant pressure sensor signal voltage drops below 1.0 Volts, which will provide me with a visible warning that my A/C system is low on refrigerant whereby I can turn off the toggle switch to prevent damage to the compressor. I provided this A/C pressure sensor signal voltage by solder splicing a wire (white in image) into PCM C1 pin 26 wire and connecting the other end of the wire to my Interceptor analog 1 wire.
The Annunciator only accepts whole number settings and 1.0 volts happens to be about the static A/C pressure on my system. So, the Annunciator warning lights may come on when there is no real problem but it gives me a visual indicator and a reminder to check the analog 1 voltage to determine if A/C pressure signal voltage is too low so that I can turn off the A/C compressor.
Okay, I now can turn my A/C on and off with my toggle switch and I have provided a visual indicator to warn me if my A/C system is low on refrigerant. I have verified on my 06 SS/SC that GM did not alter the PCM’s ability to control the cooling fans based on A/C refrigerant pressure signal. I never turn my HVAC blower to the “Off” position (it is usually on low or #1 setting) thereby making sure that I always have airflow across the evaporator in case I have turned the A/C on with the toggle switch.
The beauty of the above modifications is that when I run my OEM Stage 2 PCM, I turn the toggle switch to the “Off” position and restore full PCM control of the A/C compressor clutch relay.
My Nitrous install will follow in another post.
Amber and White wires solder spliced into PCM circuits
PCM C1 terminal pin identification
View of PCM and wiring after modifiacation showing no visible modification
Last edited by mcwarren; 09-23-2007 at 11:41 PM. Reason: spelling error
09-16-2007, 02:24 AM
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Brilliant!! Nice to see someone on the inside providing info like this. This should be stickied, I bet lots of the guys here will look at stage 3 now that they can use it and still have AC.
Also nice to see another "older" Cobalt owner posting! We be the minority!
Also nice to see another "older" Cobalt owner posting! We be the minority!
09-16-2007, 08:02 AM
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thats awesome. im deffinetly getting me a stage 3 pcm now. does anybody have any dyno charts of the gm stage 3 to show what the a/f ratio is so that we can know how small of a pulley to go with it?? this should deff be a stickie and +rep for you deffinetly.
09-16-2007, 11:37 AM
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09-16-2007, 11:57 AM
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Thanks for the "attaboys"! I hope the information proves helpful.
Yeah, I never outgrew "Hot Rods"...I'm 63 going on 16...See my sig for "my other ride". I purchased my SS/SC in an attempt to have performance and decent fuel mileage in a daily driver and it has exceeded my expectations.
Yeah, I never outgrew "Hot Rods"...I'm 63 going on 16...See my sig for "my other ride". I purchased my SS/SC in an attempt to have performance and decent fuel mileage in a daily driver and it has exceeded my expectations.
09-16-2007, 12:33 PM
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Thanks for the "attaboys"! I hope the information proves helpful.
Yeah, I never outgrew "Hot Rods"...I'm 63 going on 16...See my sig for "my other ride". I purchased my SS/SC in an attempt to have performance and decent fuel mileage in a daily driver and it has exceeded my expectations.
Yeah, I never outgrew "Hot Rods"...I'm 63 going on 16...See my sig for "my other ride". I purchased my SS/SC in an attempt to have performance and decent fuel mileage in a daily driver and it has exceeded my expectations.
09-23-2007, 09:57 PM
#14
am i right in saying the compreesor only runs wen the A/C is on? if thats a dumb question then mybad and where u turn the A/c switch off how long does it usually take the refrigerant to drop below 1 volt is the time sufficient enough to go out and "play" and see how it runs for a lil bit, and wen u switch the toggle back on should the refigerent be charged in a matter of secs to turn it back off or would u have to wait for the pressure to rise again? And also ur a wise man that u usually dont here very much from since guys ur age arent into the "computer age" ANd i also didnt want to get stg 3 b/c of the a/c situation being as i live in hot and humid S. Carolina maybe tolerable in the spring but not in the summer and early fall.
09-26-2007, 01:44 AM
#15
That is very
creative.
Have you thought about acquiring H/P Tuners software and a laptop to adjust/input the changes/parameters/qualities you desire into the Stage 3 PCM?
No doubt more costly, but the potential combinations using the H/P Tuners might make it a worthwhile investment.
Doc
Have you thought about acquiring H/P Tuners software and a laptop to adjust/input the changes/parameters/qualities you desire into the Stage 3 PCM?
No doubt more costly, but the potential combinations using the H/P Tuners might make it a worthwhile investment.
Doc
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Smc252 (11-09-2021)
09-28-2007, 01:19 AM
#19
Somehow I'm not
surprised. It would be too logical and convenient for the SS S/C owners to have had GM use the same PCM for the Stage III as they used for the Stage II (which H/P currently has a tuning suite for). Hopefully H/P will unravel the Stage III PCM and develop a tuning suite for it.
Doc
Doc
11-26-2007, 04:16 PM
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I have heard that the A/C compressor also controls the defroster by keeping moisture out of the air blown into the cabin. Is this true? I don't really care about A/C, but I need my defroster. Also, how difficult is it to switch out the PCM's. In other words, I just really want the Stage III PCM for the N2O option. If I wanted to just put in the stage III when I go to the track, can I flip the Stage II flashed PCM back in when I don't want it in?
11-26-2007, 06:39 PM
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Ah my first post here (33yr old GM tech 
)
mcwarren, not sure on the thread pitch of the sensor vs the port for it, but why not just use an older low pressure cycling switch and allow that to control the compressor?
The old A/C systems are a pretty simple circuit to recreate
)mcwarren, not sure on the thread pitch of the sensor vs the port for it, but why not just use an older low pressure cycling switch and allow that to control the compressor?
The old A/C systems are a pretty simple circuit to recreate
12-03-2007, 06:53 PM
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I have heard that the A/C compressor also controls the defroster by keeping moisture out of the air blown into the cabin. Is this true? I don't really care about A/C, but I need my defroster. Also, how difficult is it to switch out the PCM's. In other words, I just really want the Stage III PCM for the N2O option. If I wanted to just put in the stage III when I go to the track, can I flip the Stage II flashed PCM back in when I don't want it in?
Ah my first post here (33yr old GM tech )
mcwarren, not sure on the thread pitch of the sensor vs the port for it, but why not just use an older low pressure cycling switch and allow that to control the compressor?
The old A/C systems are a pretty simple circuit to recreate
)mcwarren, not sure on the thread pitch of the sensor vs the port for it, but why not just use an older low pressure cycling switch and allow that to control the compressor?
The old A/C systems are a pretty simple circuit to recreate
Last edited by mcwarren; 12-03-2007 at 06:53 PM. Reason: Automerged Doublepost
12-03-2007, 08:30 PM
#24
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Very Nice write up, Next rainy season I can see doing this!
Love seeing Mods that use whats there & Modify it to make it want you want!
Whats that Old Saying >>> Give Me a problem & enough time & I will Solve it!
Love seeing Mods that use whats there & Modify it to make it want you want! Whats that Old Saying >>> Give Me a problem & enough time & I will Solve it!
