LS1 996 AC Troubleshooting

[pdogfly]

Ok, I thought Pin 69 was part of what got removed from the engine harness. the factory wiring inside the car has not been altered as far as the A/C system is concerned. Only the engine bay harness has been removed from the car. The enigne RPM signal now comes from the GM computer that ties into the DME Pin 78. I'm thinking the DME is looking for either a running engine or some sort of signal that it isn't getting or isn't there for the system to be properly activated.

So Pin 69 @ the DME and Pin D6 @ the AC unit are factory.

[Ahsai]

Do you have the full wiring diagram of your car? Sorry can't tell from your reply, are those two pins connected currently? If not, you need to connect them. Basically you need to restore all connections between the AC control and the DME as per the wiring diagram that was removed together with the engine harness.

[pdogfly]

Yes I have a wiring diagram of the car. The 2 pins are connected correctly, they were never touched throughout the engine swap process. Only the engine harness was removed (2 cannon plugs in engine bay).

Does the DME use things like throttle position etc... as a funtion of controling the AC in this case?

[Ahsai]

Yes I have a wiring diagram of the car. The 2 pins are connected correctly, they were never touched throughout the engine swap process. Only the engine harness was removed (2 cannon plugs in engine bay).

Does the DME use things like throttle position etc... as a funtion of controling the AC in this case?

Got it now. So pin 85@relay is still connected to pin 62@DME, right?

I think it's quite possible the DME uses the throttle position sensor (pin 44@DME) as an input because if I remember correctly, the AC compressor will be cut at WOT. Also, the other potential input could be the coolant temp (pin 74 @ DME). I wonder if the AC compressor will be cut if engine is too hot or too cold.

[pdogfly]

Yes 85 & 62 are untouched, and Pin 85 is showing 5~6v with the relay removed, and with the relay installed it shows 12+v.

Do you know what the voltage range is on the throttle position sensor...maybe I can tie it into the GM sensor which is .5~.6v @ idle and 4.5v+ @ WOT.

I do have a stock Porsche temp sensor, it has 4 pins on the sensor but I'm not sure how it should be wired.

At this point I'm going to try to find an engine harness so I can tie in as much as I can so both computers "think" they are operating normally, haha...

[Ahsai]

I do not know the throttle position sensor output voltage since mine is e-gas. However, from the wiring diagram, it looks like the sensor uses a 5v reference so I would expect the signal to be between 0 and 5v, just don't know if the voltage goes up or down when you press on the gas pedal. I think you can just give 0v or 4.5v to pin 44@DME and see if that makes a diff to your AC relay.

Temp sensor, pin 1@ sensor to pin 74@DME and pin 4 @sensor to pin 34@DME (ground). Pin 2&3 can be ignored. You should see this from your wiring diagram.

Edited May 20, 2014 by Ahsai

[pdogfly]

Cool, I'll check that stuff out tomorrow. I'm not real good at following the wiring diagram when it goes from one harness to another. when the wires end in those boxes with the letter and numbers that you chase to another diagram.

Can you tell me which pins on the engine harness cannon plugs you're referring to above?

Where are you from man? I'd invite you over and pay for all the beer if you were in Lauderdale, haha, really appreciate the guidance, helping out a ton!

[Ahsai]

Anytime! It's fun to help if I can :) I'm in SoCal.

Coolant sensor

Pin1->x59/2 pin 12 -> pin 74@DME (NTC water)

Pin4->x59/2 pin 21 -> pin 34@DME (Ground sensors)

Throttle position sensor

Pin 1->x59/2 pin 21 -> pin 34@DME (Ground sensors)

Pin 3->x59/2 pin 23 -> pin 44@DME (TV-signal)

Pin 2->x59/2 pin 22 -> pin 53@DME (5v supply)

[pdogfly]

x59/2?

Is the TV signal the coaxial cable? :D

[Ahsai]

X59/2 and x59/1 are the two 25-pin round connectors of the engine harness in the engine bay. The ones you called canons. X59/2 is the same one the crankshaft sensor is on.

Haha, I know but that's what it says in the diagram. My guess is "TV" probably refers to throttle valve.

Btw, based on the throttle valve pin out above, you can rig something up with a 5v supply (e.g., USB charger) to test your old throttle body and check the signal voltage range when you move the throttle valve so you know for sure.

[pdogfly]

Any idea why I'm getting battery voltage with Key-On at Pin 85 on the Relay, if the DME provides a ground to this Pin, shouldn't it be open w/ no voltage?

[Ahsai]

Its the voltage from pin 86 via the coil you are seeing.

[pdogfly]

With the relay removed even, the pin (85) going to the DME is showing 5~6v, why would there be positive voltage if this is the wire that is supplied a ground via the DME when commanded "ON"? Shouldn't it be an open circuit with the A/C off, neither grounded or any positive voltage supplied?

[Ahsai]

No, because its driven by a transistor. Without load, the voltage reading usually is not conclusive anyway due to the nonlinear nature of solid state circuits. What matters is with a good relay connected whether it can supply a solid ground to that pin.

[pdogfly]

Well I did get another AC relay...used albiet, but just for testing I guess. Hopefully will have the system serviced back up tomorrow and be able to check the new relay and see if it really was that simple. We'll see...

If it doesn't work I'm going to take it to the dealer or to a Porsche specialist in the area to see if they can hook up a scan tool with the ability to test the circuit to see if the DME or AC control unit is faulty I guess.

Edited May 27, 2014 by pdogfly

[amille28]

I have the same issue. I'm not getting any voltage to the ac compressor. what was the resolution?

[gtxracer]

I have this same issue and was hoping to find the solution here. I’ve come back to this thread a bunch and am hoping someone can explain the solution or even next steps.

 

My situation is same as OP, LS1 swapped 996.1. I’m not getting the correct signal form pin 69, the snowflake button does give a 12v PWM signal but it’s very low current, can’t even trigger a relay. I believe this is the correct signal, but I’m curious if it’s actually a ground signal which is common in German cars. 
 

Any insight would be appreciated!

[D]

On 6/25/2024 at 5:05 PM, gtxracer said:

I have this same issue and was hoping to find the solution here. I’ve come back to this thread a bunch and am hoping someone can explain the solution or even next steps.

 

My situation is same as OP, LS1 swapped 996.1. I’m not getting the correct signal form pin 69, the snowflake button does give a 12v PWM signal but it’s very low current, can’t even trigger a relay. I believe this is the correct signal, but I’m curious if it’s actually a ground signal which is common in German cars. 
 

Any insight would be appreciated!

 

 

Alright I'm coming up to this part of my build and figured this is the cleanest thread to wrap my findings up in.  My car is still on the lift but is getting closer to the first fire up and I'm determined to have the AC system working as the Porsche gods intended before it comes off the lift.

 

Firstly - summing up my understanding of the AC Relay located behind the rear seats on Relay Support 2 (in a dumbed down version so that even I can understand it):

 

A relay is just a physical switch controlled by an electromagnet (coil).  On the AC relay the coil is controlled by the DME.  Pin 86 should see 12v+ when the key is on - this is the 12v+ side of the coil.  Pin 85 is the DME side and will see this same voltage potential between it and ground since it's just the other side of the coil.  Pin 85 goes to the DME at pin 62 where the DME grounds it when it wants to call for the compressor to activate.  This closes the coil circuit and activates the physical switch in the relay.

 

Pin 30 is the 12v+ side of the physical switch and will show 12v+ when the ac pressure switch (located in the front of the car under the passenger side cowl) is happy and fuse D6 is happy.  Pin 87 is the compressor side of the physical switch.  When the switch is closed (DME calling) the 12v+ is provided to the compressor and in a OEM porsche setup is grounded through the compressor housing to the engine activating the compressor and giving us cold luscious air.

 

The Relay can be tested by shorting pin 85 to ground which activates the coil and closes the switch.

 

 

 

Now... I have a buddy who works for Porsche and before he was promoted to his current position he worked as a tech back in the 996/997 days.  I asked him if he could provide some insight on what parameters the DME needs to see to call for the compressor.  I'll sum up our text conversation below:

 

ME: Long time no chat. Searching for some info and this might be a long shot but... I'm wondering exactly what inputs the 996 DME needs to see to decide to power the AC compressor. I've got all the wiring diagrams and understand that bit but we're (I'm in a group who are looking for the same info) not seeing the DME provide a ground to pin 62 (comp on) which signals the ac relay to send 12v to the compressor. Does the DME need more than rpm? Throttle position, coolant temp, phase of the Moon...? Trying to have the Porsche oem side run the gm ac compressor independent of the gm ecu

 

HIM: Hey man! It has been a while!  Looking at the diagram now, it looks like there’s a signal line from the DME to the climatatronic that is PWM. And information from the Instrument cluster to the climatronic cu for vehicle speed, engine speed and immobilizer. 

 

ME: So if the cluster is showing outside air temp, coolant temp, rpm, and speed correctly it will report these values to the Climatronic via a PWM signal. Then as long as the intake temp (is this the iat or the ambient via the sensor on the front of the car do you think?) is over 3.5 the DME will call for the compressor to activate provided the Climatronic is asking the DME for it?

 

HIM: Yeah, so as long as the instrument cluster is happy with all of those, the data will be sent on the k line to the climatronic. It’s been a long time, but I think the k line is a LIN bus. Input to the climatronic on A1 marked k lead in the diagram.  Intake air sensor I think is on the intake pipe to the engine, it should go from there? I think.  Haha. Little bit of a puzzle to figure out how to trick it! 

 

ME: Any mention of the DME not calling the compressor because of the throttle position? I.e. No ac at wide open throttle? 

 

HIM: No mention in the SIT book, but I know 997 and later cut the ac compressor under full throttle.

 

__________________________________________________________________________________________________

 

So - if the relay is working correctly and has 12v+ where and when it needs it, and the cluster is showing speed, rpm, coolant temp, and outside ambient temp, and the DME is seeing the (assumed) Intake Air Temp, and this intake air temp is above 3.5C, and the climatronic is calling for AC (snowflake on), the DME should ground pin 62 which closes the coil on the relay which provides 12v+ to the compressor turning it on and blessing us with cold air out the vents on to our hot, sweaty face.  Ohhh that's nice.

 

I am not certain that TPS reporting correctly to the DME is required for the system to function.

 

My car is a few weeks out from being able to test any of this but I thought I'd post here so someone else can sanity check my logic or demonstrate that the above does or does not work.  Hope this helps someone!

 

Cheers!

 

 

 

Edited January 15 by D
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