LS1 996 AC Troubleshooting

[pdogfly]

I believe I have everything hooked up and wired correctly but I'm not getting voltage from the relay when the AC *Snowflake* button is pushed on the climate control unit.

I've checked the wiring diagram. One of the 2 wires connected to the 87 pole on the AC relay (on Support 2) goes to the engine harness cannon plug (Pin #23). I took that wire all the way to the compressor (+) lead. On the wire diagram, Pin #25 is also drawn near by #23 where the compressor lead is...anyone know what that is for? (See attached...)

Got the system charged today, and with a full charge ... the compressor would not engage. Verified there was no voltage at the compressor. To see if the compressor would engage, I jumped it with 12v(+) and got the compressor to engage and indeed it is blowing cool air!!

So I'm wondering why this isn't being done automatically by the climate control unit?

Also pin #69 on the ECU harness says "A/C Compressor Requirement"...any idea what this means? Does it need to be hooked up to something?

I thought maybe there was no RPM being detected by the Porsche ECU which may have been the issue, but I double checked and the output from the GM computer is sending the correct signal to the RPM input on the Porsche ECU.

Attempted to swap some relays around on the #2 support next door to the ECU...no joy. No voltage being sent out of the 87 pole on the relay. There is voltage being supplied to the relay though...

Any help would be appreciated...I hope it's just maybe a simple bad relay or pressure switch. But if it isn't, what could it be?

I haven't verified that the AC pressure switch is working correctly. And I haven't traced and seen which other wires associated with the AC relay go to or do.

I'm a GM guy and familiar with their scanning capabilities, if I take the car to a Porsche dealer, any idea what they would charge to do a diagnostic to see if the pressure switch is working properly or to maybe see if the AC button on the control unit just may simply not be working? The 'Snowflake' appears on the unit when the button is pressed...just no relay action to send 12v to the compressor.


Thanks,
Patrick

[Ahsai]

Welcome to Renntech. Can you tell us the year and model?

I have not checked the wiring diagrams yet but most cars have a low pressure sensor and a high pressure sensor, which will cut power to the compressor if either is tripped.

Just a few thoughts that came to mind.

How did you charge the system without running the compressor or you just jumped it while charging? How much refrigerant was put in?

I could be wrong but if the outside temp is lower than some number, the compressor will not turn on. Maybe that input is lacking?

Edited April 17, 2014 by Ahsai

[Ahsai]

Ok, checked the wiring diagram now. That pin #25 is telling you that the connector has a total of 25 pins. Irrelevant to the ac.

If you remove the compressor relay and push that ac button, what are the voltages you see at pins 30, 86 and 85, relative to ground?

What is the voltage between pins 85 and 86?

If you don't see 12v at pin 30, power is not reaching the relay and next upstream stop is the pressure sensor.

If you don't see 12v between pins 85 and 86, the DME is not commanding the compressor to turn ON. This will be a much tougher problem due to your LS1 conversion.

If you have durametric, you can trigger the DME to turn on/off the compressor, which will test the integrity of both the control and power of the compressor circuit.

[JFP in PA]

Welcome to Rennlist.

Ummm......How about "Welcome to RennTech"! :welcome:

[Ahsai]

Welcome to Rennlist.

Ummm......How about "Welcome to RennTech"! :welcome:

Lol, sorry. Corrected now. I've been jumping between the two forums a lot lately.

[pdogfly]

It's a '99 C2 Carrera.

The AC system was hooked up to a servicing machine that pulled a vacuum on the system and then put the required 1.95 lbs of R-134a freon in via pumping it in with out the car running. I know it had a full charge from the gauge readings. Once I started the car and pressed the AC *on* button...nothing happened. Then applied 12v to the power wire of the compressor and it did work, clutch engaged and it started pumpin and cold air was blowing while the compressor was working for the time we had it jumped to 12v.

I haven't checked any voltages with the relay removed. I do know that there is power being supplied to the relay, can't remember which pin off hand. Just no actuation at the 87 pole which is the wire hooked up to the power supply side of the compressor.

I talked to my brother who's a good mechanic and he said that some forign cars provide Ground (-) to some accessores to complete the circuit. Any idea if this is the case with Porsche AC Compressor signaling?

When I'm able to look at it agian I'll see what the voltages are with the relay removed at the numbered pins...

I talked to a Porsche service provider and they said that scanning the computer would not tell him if the AC pressure switch was good or bad?? Is there a procedure to bypass the pressure switch? I tried to use the paper clip method to close the circuit that I saw on the diagram that should be closed in order for it to work...ended up blowing the blower fan fuse! Ugh...

What is DME? ...in aviation it's Distance Measuring Equipment :-P

I'm not sure what a Durametric is??

I know the compressor works, just need to figure out what's going on with the signal that controls it. I know there is a low and high RPM window that it will operate too, and I want to keep that functionality so it works like it was on the factory engine.

Hope to have this sorted out soon! It's not getting any cooler in S. FL!!

Thanks,

Patrick

[Ahsai]

The compressor ground is the engine itself since the compressor is mounted directly metal to metal on the engine. Same is shown in your diagram if you look carefully...there's a "arm" coming out to the left, which is the ground. That's why the compressor power is a single wire (12v positive).

DME is Digital Motor Electronics, same as ECU. Porsche calls it DME. It supplies signal to activate the compressor relay. The DME itself gets command from the ac control panel. The DME controls the compressor because in some cases it needs to turn off the compressor even ac is ON e.g., under wide open throttle.

One more question. How do you generate the 60 teeth (with 2 teeth missing) rpm signal the DME is expecting?

Forget about Durametric. We can still keep diagnosing the system without it as long as you can access the DME.

[pdogfly]

I have the RPM signal output from the GM computer tied into the RPM input to the "DME". I've had the GM computer re-flashed with a 6 cylinder output signal. The RPM on the tachometer is right on and displays correctly. So I know it's getting an accurate signal.

I'm not sure if it may need additional information though, seems apparent... Like pin #69 that is labled "A/C Compressor Requirement" I have no idea what that is.

I haven't had any diagnostic scanner tool/computer connected to the DME to see what is going on with it. I'm sure it thinks its insane with the stock engine harness missing. :-P

[Ahsai]

I see. DME pin #69 is called "AC demand" in my wiring diagram ( Bentley repair manual). It's the signal line that goes from the climate control to the DME to ask the DME to turn ON/OFF the compressor.

[pdogfly]

Hmmm...well I won't be able to take another look until Friday or Saturday this coming. I'll post back up when I get a chance to put a meter on the relay poles. I wonder if throttle position needs to be seen by the DME for this to work?

[Ahsai]

Hmmm...well I won't be able to take another look until Friday or Saturday this coming. I'll post back up when I get a chance to put a meter on the relay poles. I wonder if throttle position needs to be seen by the DME for this to work?

It's hard to say unless someone knows the exact inputs the DME needs to operate the ac compressor. That's why I hope your problem is on the power side and not the control side, which the tests on the relay will tell us.

[pdogfly]

Ok...provided the AC relay is as depicted below, which I think is correct here is what's going on...

Pin 87: ohms out to (-)Ground at all times

Pin 87a: ohms out to (-)Ground at all times

Pin 85: (+)12v with key on

Pin 86: (+)12v with key on

Pin 30: Nothing, no signal, neither ground or +12v with AC button ON or OFF.

With engine running and AC button cycled on and off, there is no action at the relay. Sooo I'm not sure where to go from here...help. :)

Thanks,

pg

[pdogfly]

Looks like the 30 pole goes to the Pressure switch, the 87 pole goes to the compressor and to the control unit.

Not sure where the 85, 86, or 87a pole wires go...

Thinking mayyyybe a bad pressure switch? Since the 30 pole shold show a ground when the switch is within pressure range? But the voltages and grounds where they are don't make much sense...just thinking out loud.

[Ahsai]

Ok...provided the AC relay is as depicted below, which I think is correct here is what's going on...

Pin 87: ohms out to (-)Ground at all times

Pin 87a: ohms out to (-)Ground at all times

Pin 85: (+)12v with key on

Pin 86: (+)12v with key on

Pin 30: Nothing, no signal, neither ground or +12v with AC button ON or OFF.

With engine running and AC button cycled on and off, there is no action at the relay. Sooo I'm not sure where to go from here...help. :)

Thanks,

pg

Pg, looks like you have problems on both the control side and the power supply to the compressor.

A/C compressor relay

Pin 87 -> compressor -> ground

Pin 87a: disregard

Pin 85 -> pin 62 of DME "Comp ON"

Pin 86 -> +12v whenever key is ON

Pin 30 -> pressure switch -> pin 87 of "Actuation Heating Relay" -> Fuse D6 -> battery +ve

You need to check the following:

1) Does Pin 85 supply ground when a/c button is pressed? DME supplies ground to power the compressor relay. If not, DME is NOT commanding the compressor to turn ON.

2) Check fuse D6.

3) Key ON. Check pin #4 of pressure switch for 12v. If OK,check pin#1 of pressure switch for 12v. If no 12v at pin#1, pressure switch is BAD. If no 12v on pin#4, check pin 87 of "Actuation Heating Relay" (Relay #18 on the front driver relay panel) has 12v with the relay still plugged in.

[pdogfly]

Pin #85 is showing +12v with key on at the moment.

Well I hooked up a set of gauges and after sitting for almost 2 weeks since I charged the system....it's showing ZERO psi. :( Obviously have to find the leak and fix it before I can troubleshoot any further. Siiiiigh.

Fuse D6 and Relay #18 are good and 12v is coming to Pin #4 on the pressure switch. And there is nothing on Pin#1, likely due to the system being unpressurized.

The saga continues...

[pdogfly]

Just an update... I replaced the o-rings in the condensors and on the receiver/dryer. I am also switching to a compressor for a GTO. The pressure ports on the compressor are on the side instead of the back, and it is new/remanufactured. I don't think the compressor that was on there was leaking, but just something I wanted to do anyway because the lines were really close to the exhaust manifold with the adapter fitting on the back of the F-Body (Camaro/Firebird) compressor. Hopefully will have a chance later next week to hook everything back up and vacuum the system down again to check for leaks....

Stay tuned... :)

[pdogfly]

Got the GTO compressor installed, needs a longer belt, and a different adapter than what I had...always something. I swear when the AC is working like it should I'm gonna pop a bottle of champagne. :-D

[pdogfly]

2 o-rings that connected the custom lines to the factory lines were the culprit! :oops: I guess I didn't check them thinking they were on good when I attached them initially. they were damaged at both tops on each line so no liquid/oil was present upon inpsection. System is under a vacuum now and will check it in the morning and then hopefully service it and continue trouble shooting the compressor control circuit. I was getting ready to replace the evaporator and not looking forward to that. We'll see in the morning, hopefully the gauge hasn't moved. :wrench:

Edited May 19, 2014 by pdogfly

[pdogfly]

Alllllrighty then. Just serviced the system with 2lbs of freon (3 12oz. cans). With the compressor jumpered and engine at idle, cooling fans on high, it is blowing cold. :thumbup: Used vac pump to suck down for 15m before servicing.

Checked the pressure switch and with key on and 12 volts is present at both pins #1 and #4 so that tells me that the switch is ok. Still no joy with the AC button on the control head unit on the dash. I'm going to check the relay readings again and wil post back...

[pdogfly]

Ok, here's what is going on @ the A/C Relay currently...

Pin 85 (pinkish wire with green stripe) & 86 (red wire with blue stripe) are both showing 12+v with engine running, AC button on or off.

Pin 87 (green wire with yellow stripe) is ohm'ing out to GND with button on or off.

Pin 87a (brown wire) is also ohm'ing out to ground.

Pin 30 (purple wire with yellow stripe) is showing 12+v with engine running, AC button on or off.

Edited May 20, 2014 by pdogfly

[pdogfly]

With the relay removed Pin 85 shows 5~6v, everything else is the same... Not sure why Pin 87 and 87a are both ohming out to ground? :cursing:

[pdogfly]

Ok...I disconnected the plug from the compressor and Pin 87 is no longer grounded. The GM compressor has 2 wires coming off of it, in theroy one (+) and one (-). With either wire connected to ground, the opposite wire will ohm to ground as well.

I had it set up with the Pin 87 wire running to the (+) wire on the compressor, and the "ground" wire on the compressor....grounded. Essentially grounding Pin 87. I'm not sure if the OEM Porsche Compressor is a single wire or 2 wire compressor. But this may shed some light on the situation....

[Ahsai]

The stock compressor has one wire connected to positive and it uses the compressor case as the ground. The way you setup your two wire compressor sounds correct. Your issue is on the control side that the DME is not grounding the relay even when the AC button is pressed.

[pdogfly]

Faaantastic. Suggestions on where to go from here? Could it be the A/C head unit? Find someone with a durametric?

Your input is much appreciated...just wish I could figure this gremlin out.

-pg

[Ahsai]

The problem gets significantly harder since it's on the control side and I don't know you custom wiring of the DME. How's the wiring between the AC computer and the DME? e.g., pin 69 of DME is supposed to connect to pin D6 of the AC computer.