DCD

Have been trying to sort out my 95 993's air con and mixer valves and have a few questions.
First, I recently had some freon added to the system. After that I could confirm the compressor was doing it's job.
I could feel cold air coming out of the vent on the far right, all other vents were pumping out heat.
This led me to looking at the mixing valves in the footwells, and I found that the left side valve was completely open at all times. The PCB and contacts look to be burnt and impossible to repair.
After closing the valve, I reinstalled it into the car, but didn't connect the electrical connector to it as it would do no good anyway.
I tried the AC the next day, but didn't get anything at first, then after awhile the volume of air suddenly increased as if it was working again, it switched on and off several times and then I shut it off. After that I checked if the compressor was working and it doesn't come on, even though I have enough pressure in the system.

Could this be because I had unplugged the foot well valve, is the system sensing something missing, so it's stopped working?
Or, is it something else?

I am also wondering if there is any difference between the 993 and 964 servo motor, identified as 993 624 325 00 and 964 624 325 00, can I use the 964 part as a replacement?

At the moment though I'm quite pleased I can drive around without getting hot air constantly blowing into the car, so we are on the way!

Any advice greatly appreciated.

911RufRT

I would start with looking at this link

http://www.porschehvac.bergvill.com/


I dont think you can use the 964 part number for the lower servo motors. I replaced one of mine recently and I was able to find one used on ebay for about $70. There has been other used ones for sale before on this board.

ToreB

Thanks for the link 996Carrera.
I have never seen any shutdown or strange behaviour in CCUs if the servo's are disconnected. To my knowledge, failure in either potentiometer, motor or plain disconnecting it will be sensed, all motion stopped, and a fault code will be stored.
As for your fault now, you mention that your system turned on and off, do you mean that the blower fans shut off and on again? That might be caused by a damaged rear fan, if your temperature **** is set to anything but coldest setting. My website tells you why.

As far as I know, all 964 and 993 servos are basically the same, but there's different gears and lever arms fittet to them, according to their position. I would therefore think it's possible to use a any servo anywhere in the car, but you may have to use the output shaft, lever arm or similar from the damaged servo.
Cheers,
Tore

DCD

To clarify what happened, I pushed the big snowflake button and the things that normally happen, happened, but as I was driving along a few moments later, suddenly the air volume increased quite alot. It then cycled from a higher volume to a lower volume a few times during the next 10 minutes, so I thought that's not right and shut it down.

I suspected that my freon levels might be just a bit too low so that the compressor was cycling in and out. It could indicate a leak in the system too I suppose, although I did check the pressure when I arrived at home and it seemed OK.

Ah, that's good that the 964 and 993 servo parts are interchangeable, I expected they should be as it's the 60 degrees or 120 degrees that matters.

I have a USB OBDI cable that I previously used for a VW Golf, would this also work with the 993 and the analysis software Scantool to find out if any other elements of the system are faulty?

Thanks for any advice!

ToreB

Any cycling of the compressor would not affect the air flow. Problems in the air flow at constant fan speed are caused by inert/defective servo flaps or problems with the resirculation flap. I suspect you have a problem with the resirc flap, see detailed explanation on this is given on my HVAC page.
A VAG-Com OBD cable and corresponding PC software might enable you to establish contact with the Motronic engine control, but not the other OBD-enabled control units in your car.
The Rennlist Scantool PC SW freeware need a special home made serial adapter or USB type as my T-OBD interface.
Cheers,
Tore

DCD

I believe you are probably right about the recirculation flap as after reading your site I have occasionally heard a whoosing sound during deceleration which I hadn't connected to this system. I thought I might have a fan belt needing adjustment.

DCD

Looking forward to your T-OBD interface being available again then to verify what's wrong.

ToreB

Thanks DCD, I'll have the new batch of T-OBD's ready in mid september the latest.
Drop me an email and I'll inform you when ready. Mail address on my web site.
Cheers,
Tore