Build Thread: '99 C2 996 LS1 Swap
#256
Looking at the AC system and radiator fans.
Found the AC trigger wire in the engine bay, I had tucked it into the harness sheathing. Green wire with yellow stripe.
I also found the Porsche high side AC hose. I’m going to attempt to have a local AC shop make me a custom hose. If not I might cut and TIG weld.
I found the #12 pin blue wire on the top X51 plug. This had 12v signal with ign on. This is not routed to the alternator but I don’t have a battery light on the dash.
I do, however, have a CEL which is likely from the tach not working. I believe the DME needs a crank signal from the LS engine to work the tach and allow the DME to trigger the radiator fans. I have the P car water temp sensor in the LS1 head. I also have new radiator fans and resistors installed. I jumped each relay and confirmed all 4 fan speeds work in the relay module (2 hi and 2 lo). Other 996.1 LS swap guys say their fans work via the sensor but mine do not appear to be working when the engine is hot. The gauge does read lower than the LS sensor shows on the Holley Terminator X readout. I recall the 996 fan kick on temps being somewhat high and others have ran wires from their LS standalone harness to bypass the P car relays. I might have to give this a try to activate my fans and control the kick on temps myself.
I’m looking for advice on where to splice into the chassis wiring with my tach signal. I have a tach converter box to convert 24x signal to 58x essentially.
Found the AC trigger wire in the engine bay, I had tucked it into the harness sheathing. Green wire with yellow stripe.
I also found the Porsche high side AC hose. I’m going to attempt to have a local AC shop make me a custom hose. If not I might cut and TIG weld.
I found the #12 pin blue wire on the top X51 plug. This had 12v signal with ign on. This is not routed to the alternator but I don’t have a battery light on the dash.
I do, however, have a CEL which is likely from the tach not working. I believe the DME needs a crank signal from the LS engine to work the tach and allow the DME to trigger the radiator fans. I have the P car water temp sensor in the LS1 head. I also have new radiator fans and resistors installed. I jumped each relay and confirmed all 4 fan speeds work in the relay module (2 hi and 2 lo). Other 996.1 LS swap guys say their fans work via the sensor but mine do not appear to be working when the engine is hot. The gauge does read lower than the LS sensor shows on the Holley Terminator X readout. I recall the 996 fan kick on temps being somewhat high and others have ran wires from their LS standalone harness to bypass the P car relays. I might have to give this a try to activate my fans and control the kick on temps myself.
I’m looking for advice on where to splice into the chassis wiring with my tach signal. I have a tach converter box to convert 24x signal to 58x essentially.
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gtxracer (07-26-2023)
#257
Rennlist Member
Thread Starter
3 dme pins are the basic ac control .pin 14 ground signal from pressure switch-pin 69 climate control turn on ac -pin 62 ground signal to ac relay .Don't think the ac kit you reference will help -looks like a total rewire and does not handle thepwm signal from climate control .The easy button is put a ground switch on the pin 62 wire and activate ac relay .I would still explore if terminator can handle a pwm signal and have a seamless operation
Seems like if I use the Porsche 12v signal I'd need to step down to 5v. I have a diode on the way for the 2 pin GM plug pigtail as well.
I believe we want to feed pin 78 the LS crank signal, but when I did this last time it did not show on the tach. Pin 80 is speed signal output, and pin 79 is speed signal from ABS control module. I don't want to tap into pin 79, I want the DME to control ABS, but pin 79 likely needs signal from 78 to run properly and this should flow to pin 79 and 80. I'll test this soon.
#258
the snow flake is a 12 volt pwm signal .If the terminator has provision for a 12 volt pwm and can convert to a to either a ground signal or a voltage signal you have options.Pin 14 is ground from low pressure sensor and is insurance that the system has freon .Example -wire from pin 14 to new relay pins 86 and 30 -if positive voltage from terminator to pin 85 .Pin 87 ground signal to ac relay to turn on compressor .
#259
Nordschleife Master
Mk1 the dme does not control the abs. There is no canbus. That is just a signal output to the dme and should not effect the abs.
I do beileve the dme has to see rpm but it doesnt matter what rpm to kick the compressor. If the dakota digital allows the dash tach to read then its corrected so u ahould be able to send that corrected signal to the dme?
Or is the issue that the dme changes the signal to the dash and the dakota wont send the correct signal to the dme?
I do beileve the dme has to see rpm but it doesnt matter what rpm to kick the compressor. If the dakota digital allows the dash tach to read then its corrected so u ahould be able to send that corrected signal to the dme?
Or is the issue that the dme changes the signal to the dash and the dakota wont send the correct signal to the dme?
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gtxracer (07-18-2023)
#260
On wide open throttle I believe the dme shuts off the ac compressor ..How does it know ?The point being there is some code in there that is monitoring something .The other consideration is the fans -when ac on the fans need to be running.
#261
Rennlist Member
Thread Starter
the snow flake is a 12 volt pwm signal .If the terminator has provision for a 12 volt pwm and can convert to a to either a ground signal or a voltage signal you have options.Pin 14 is ground from low pressure sensor and is insurance that the system has freon .Example -wire from pin 14 to new relay pins 86 and 30 -if positive voltage from terminator to pin 85 .Pin 87 ground signal to ac relay to turn on compressor .
Mk1 the dme does not control the abs. There is no canbus. That is just a signal output to the dme and should not effect the abs.
I do beileve the dme has to see rpm but it doesnt matter what rpm to kick the compressor. If the dakota digital allows the dash tach to read then its corrected so u ahould be able to send that corrected signal to the dme?
Or is the issue that the dme changes the signal to the dash and the dakota wont send the correct signal to the dme?
I do beileve the dme has to see rpm but it doesnt matter what rpm to kick the compressor. If the dakota digital allows the dash tach to read then its corrected so u ahould be able to send that corrected signal to the dme?
Or is the issue that the dme changes the signal to the dash and the dakota wont send the correct signal to the dme?
#262
Nordschleife Master
There r low and high speed thresholds for the rad fans through the dme associated with the dme. I would guess that the logic could be entered into the terminator x? Basic math channel saying if condition 1 (ac switch on) = fan on low speed and if coolant temp > (x...dont know factory value) = high speed
#263
If you used the terminator x for the snowflake wire to turn on the compressor you will need to add a new relay because you want to keep the low pressure ground signal as a safety measure .The terminator would activate the new relay -the pin 14 wire would be the ground source for the new relay to activate the porsche ac relay .
#264
Rennlist Member
Thread Starter
There r low and high speed thresholds for the rad fans through the dme associated with the dme. I would guess that the logic could be entered into the terminator x? Basic math channel saying if condition 1 (ac switch on) = fan on low speed and if coolant temp > (x...dont know factory value) = high speed
If you used the terminator x for the snowflake wire to turn on the compressor you will need to add a new relay because you want to keep the low pressure ground signal as a safety measure .The terminator would activate the new relay -the pin 14 wire would be the ground source for the new relay to activate the porsche ac relay .
The low pressure ground signal - is this just a signal from the sensor that says system has pressure and refridgerant? If so, I think I can just find this pin (it was referenced earlier in the thread) and tie that as input to the TermX. I think I could avoid another relay doing it this way as the logic on the TermX computer will protect the compressor trigger in a low pressure situation and the OEM relay is still protecting the compressor circuit. Any issues you see with that?
Thanks for your help fellas!
Last edited by gtxracer; 07-25-2023 at 07:30 PM.
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gtxracer (07-25-2023)
#266
Rennlist Member
Thread Starter
Tore into the wiring last night for AC. Pin 69 is a PWM signal from snowflake button, and that worked as expected, so I will use that as an input to the TermX. Pin 62 is ground signal to trigger 12v+ for compressor clutch - this also worked as expected as I saw 13.X volts at the AC wire in the engine bay. Pin 62 will be a ground signal output from TermX. The AC wire in the engine bay will go to the step converter. The step down converter I found for 5A is hyuuuuuuuge so I need to find a place for that to live before I do the final wiring and test the system. Also bought diodes for the GM compressor pigtail as they're a common mod to protect the compressor internal circuit.
Waiting on a few connectors to be delivered then I can finish the wiring and test the system via a manual ground of pin 62 to engage the compressor clutch. I am also going to fix the ground on blue wire for the dash via the L pin on the alternator, I think this is necessary to have the PWM signal from the snowflake button. I am also going to send a rpm signal to pin 78 as a mirror from pin 80 (tach) in case the DME wants to see this for other functions.
I'll post again once I have more to share. I'll makea quite diagram with wire colors and post the TermX programming once I have it done. Thanks again for the help
Waiting on a few connectors to be delivered then I can finish the wiring and test the system via a manual ground of pin 62 to engage the compressor clutch. I am also going to fix the ground on blue wire for the dash via the L pin on the alternator, I think this is necessary to have the PWM signal from the snowflake button. I am also going to send a rpm signal to pin 78 as a mirror from pin 80 (tach) in case the DME wants to see this for other functions.
I'll post again once I have more to share. I'll makea quite diagram with wire colors and post the TermX programming once I have it done. Thanks again for the help
Last edited by gtxracer; 07-27-2023 at 03:25 PM.
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dcdrechsel (07-27-2023)
#268
Rennlist Member
Thread Starter
Fyi, I have been using one of these in my pickup for 10 years because the ecm output is bad. Small and it works but 3a.
https://www.amazon.com/PlusRoc-Water...hoCy9kQAvD_BwE
https://www.amazon.com/PlusRoc-Water...hoCy9kQAvD_BwE
#269
Nordschleife Master
Thanks! I'll save this one. I think the GM compressor output can be as high as 4.5A, but that was from a quick search, 4.2A here and 20A here. I think the initial pull might be 20A to start the clutch, which makes sense, but unsure how my little 5A box will like that.
No way thats a 5v output pushing 20amp. The 5v is a signal wire for the computer that tells the computer to trip the relay,
sanden compressor clutches r all 12v.
I may be wrong but have never seen what u described. I think u need to revisit. Im at watkins glen till monday so i still dont have time to dif deeper......maybe next week.
#270
Rennlist Member
Thread Starter
No way thats a 5v output pushing 20amp. The 5v is a signal wire for the computer that tells the computer to trip the relay,
sanden compressor clutches r all 12v.
I may be wrong but have never seen what u described. I think u need to revisit. Im at watkins glen till monday so i still dont have time to dif deeper......maybe next week.
sanden compressor clutches r all 12v.
I may be wrong but have never seen what u described. I think u need to revisit. Im at watkins glen till monday so i still dont have time to dif deeper......maybe next week.
Messed with the TermX logic and inputs/outputs. Have everything wired across pins 14, 62, and 69. I'll post the results soon. Just verifying the wiring of the AC kick trigger to go along with the other inputs and outputs so the TermX will trigger the fans and know when to shutdown the AC. After testing the setup, hitting snowflake triggers the compressor. My only issue so far is I don't think I'm getting a ground signal from pin 14. There's continuity across that wire at the DME, but when I tell the TermX to look for ground, it doesn't see it. If the sensor isn't working or there's not enough pressure (aka, no freon), would the sensor send a voltage or just be an open circuit? This detail is my only hangup and I need this before I can finalize and tidy up the work. I'll post a full rundown of how I accomplished everything including the programming and logic of the TermX once I get this detail ironed out.