rodgerdodger

I have a very similar setup, i kept the 996 engine harness and just used the connections i needed and deleted the rest. I T-eed the Pcar crank sensor input on the harness to the LS crank position sensor. I also used the terminator to take over the fan controls.

gtxracer

Thank you! DME is a 99. Front fans driven by the Terminator X PCM. Yeah, high/low switches still go to the DME.

Got it, thank you. So pin 14 is the switch signal, that's good to know. Pin 69 would have a signal from AC snowflake button. Pin 62 is another ground signal - sounds like DME would trigger this and that's what I'm missing to trigger AC compressor. Yeah, the AC kit I linked would be a total rewire and I don't want to deal with that if I can help it. Terminator X could give a +5v pwm signal I believe. The Porsche signal is 12v, unsure if pwm. Unsure how to get the Terminator to trigger 5v pwm based on Porsche trigger signal from either pin 62 or pin 69. I can pull back the subwoofer box and carpet to manually ground pin 62 and see if I get 12v at the green/yellow wire in engine bay.

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.

Thanks for chiming in. I also used the 996.1 engine harness and deleted the extra connections. When you T-eed the Pcar crank sensor input to the LS crank sensor, did it make the tach work? That should be pin 78 if your car is also a 996.1. I went straight to the tach at pin 80.

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.

dcdrechsel

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 .

De Jeeper

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?

dcdrechsel

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.

gtxracer

Got it. I bought a 12v to 5v step down for the GM compressor, I'll need this if using the Porsche signal. Terminator X can trigger a ground, 5v, or 12v signal in the outputs, so I think it can trigger anything we want. Ex: TermX ground signal to pin 87 and 14. This would trick the system, not sure if this is a great solution as I believe there is a separate fan for the condenser that also needs to be triggered....unless this does that as well.

Ahh, got it, good to know about the MK1 DME and ABS. Yes, I want to send the corrected tach signal to the DME, I believe this is pin 78. Last time I tried this, I didn't get tach working, but I recall the box wasn't setup right anyway and I think I should try this again.

De Jeeper

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

dcdrechsel

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 .

gtxracer

Yeah termX is running the fans based on LS sensors and grounding out the relays at the DME. I found the inputs and outputs on the TermX software and was playing with it the other night. There's a couple funny logic paths that I don't quite understand, but I need to do a bit more research and find time to tear apart the car. Now that I have another DD again, I can get started.

Yeah, this is the plan. Hit snowflake, take signal from this wire as input for TermX, then TermX output can be run to either a) compressor directly (too much current I think, 4.5A for compressor and max TermX is 3A) or b) run TermX output wire to AC compressor trigger wire (ground activation of relay, I believe). I'm leaning towards B, essentially bypassing the DME with the TermX computer. I think the Porsche compressor trigger is 12v, and I have a 5v step down now to route in between the GM compressor.

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!

dcdrechsel

B is good - I don't know the terminator x capability so can't comment on low pressure ground signal connection to terminator x .

gtxracer

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

De Jeeper

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.

gtxracer

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 will like that.

De Jeeper

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.

gtxracer

Did a little digging, yes, I believe the compressor is 12v. Unsure why I thought it was 5v pmw, but I'm glad you said something!

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.