leeshephard

Hi

I am in the middle of the dreaded AC diagnostics and wondered if any one could tell me if the output from scanntool should be like below in the attached image? I am not getting any changes in the variables highlighted in red - these just happen to be the AC functions...

Would really appreciate if someone could clarify what should be in these fields and weather I should see them change when I activate the AC switches.

Cheers!

nine9six

Lee,

Maybe try refreshing the scan of the A/C system?

Exit that portion of the scan software, turn on a/c and rescan.

Or

Completely exit the software, start car and a/c and re-initiate the software scan of the a/c system.

You could also try setting the software to scan a 964?

It would be helpful if you ID year and model of your car.

leeshephard

Thanks nine9six, I have tried all those things many times over the last 6 weeks I have been working on this, I just wanted to see if there SHOULD be anything in those boxes and if so what. This might help me discover the issue I am having.
My car is a MY 96 993.

Thanks again for your help!

nine9six

I'm so sorry I couldn't be of some real help. I have a Durametrics scantool, but cant remember if those switch fields should be populated. You can try looking into Tore Bergville site, if you have not already done so. Heis unequivocally the site guru on all things HVAC!

HTH

http://www.bergvillfx.com/porschehvac1

BobbyT

Hi Lee,

If you're using T-OBD, you may want to check that the switch on the OBD port connector is set in the CCU position, and the same selection is made on the computer screen. Then try "clear" and "refresh" and you should be able to run through the tests and see actual values.

Rockit

What is the symptom with the A/C, what is happing.

leeshephard

Thanks everyone!

I am using an ODB interface I made from a kit years ago, I think the design was on here somewhere. Its the same circuit that Tore includes in his T-OBD documentation. It has worked AFAIK for every other module fine.

The issue I have is that my AC conendser fan AND compressor are intermittently activated. All other signs that the AC is on are there - AC or MaxAC buttons pressed and lit up. I have checked freon levels with a dual manifold guage etc. When the AC is on it is withtin spec's for vent temp and also low and high side pressures. I have also confirmed that the 3-way pressure switch is OK.

When the car is on and the AC is set to run but not working I have probed the pins on rear connectors for the condenser and compressor relay (K24 and K23). As I understand it these should be switches to GND when they are turned on buy the CCU. Mine were at 13.9v which means the CCU has not activated them. I then probed while the AC was working and those pins did go low to GND. So it looks lke the CPU inside the CCU is just not turning it on :-(

I also ran through the TEST program which allows you to activate each servo and fan in turn. Everything on my system worked! including lo/high speeds on the oil cooler, ac condenser and rear blower fans.

The only thing that is weird is that in the 'ECU Inputs' page it shows nothing for those switches - it's like the CCU is not getting told to turn on the AC!

I then decided to check the front panel switches - I clean out the AC switches and circut board plugs. I then took DMM measurements from the pins of the switch back to where I could find on the ribbon connector and they seemed to be connection OK. I am trying to work out the circuit further so I can trace all the way back to the microprocessor on the main board.

Any help is gratefully received - I am running out of options

leeshephard

Forgot to mention, my CCU is a 993.659.047.01

pp000830

bad pressure switch/sensor ? If the system is working the compressor cycles as normal.

leeshephard

Thanks pp000830
I have checked and confirmed the correct operation of the switch. If it had failed it would not stop the condenser fan running - it would just not run in high speed.

What I really need to check is if my scan tool app is working as it should, can anyone confirm weather the 'snowflake' switch settings are updated in the 'ECU Inputs' window in scan tool?

Cheers

Lee

AllMine

I just checked. My 95 never shows anything in the top right boxes other then off. I did see some values in the bottom left boxes. But basically nothing changed...ever. Actually while i was scanning the climate control unit the cars HVAC unit is completely un responsive. I do have codes I thought would be there though. I only have about 30 minutes of play time with the scanner... not real impressed...then again I only paid 100 bucks or so and am comparing it to the multi thousand dollar Autel and Snap-On scanners I uses daily at work.
Curt
I started with the a/c buttons off...scanned...nothing but off in the top right boxes.
Scanned Motronics...HVAC unit came alive.
Turned on both A/C buttons...scanned...nothing but off in top right

ToreB

I have seen incompatibility issues in Scantool regarding the Input and Actual Values screens. I have not done a lot of research on this, but guess the software isn't compatible with all CCU versions.
The Porsche diag tools show "live" values of these settings, i.e. they change as you press the buttons or alter the sensor inputs.
Cheers,
Tore

leeshephard

Curt - Many thanks for your efforts! I guess my CCU may have another issue then :-\

Tore - Thanks for the additional info, I'll be contacting you shortly to arrange a repair!! :-)

geldgrube

I can confirm what Tore is saying. On my '95, the input values were reflected in Scantool but on my '96, they are not. Does anyone out there have the Scantool source code? I wouldn't mind taking a shot at addressing some of its issues.

IainM

So you're not showing any codes either? That would point to a comms failure
are the other modules reading Ok? Getting serial numbers back for them etc?

my CCU repairs have all been facilitated by T-ODB code pointing directly to failed part