ToreB

The fresh air and mixer servos move constantly when the ignition is on to keep the desired cabin temp, and these are thus the ones that will fail first.
As far as I know are there no spare servo motors available, and you need to change the PCB as well. PARTisan does this very well.

The 986/7 and 996 are using a similar type of servo motors, (as in most VW/Audis) so they will probably wear out in time too.
Cheers,
Tore

993c4ie

As i am having problems with air/temperature regulation in the cabin of my 1995 993C4, i removed the CCU unit, opened it, clean it, mesured few things, and fit it back.
Yesterday, i decided to remove the mixing valve located in passenger footwell. I tested it on a bench. All working well, and resistance value follows valve position.
Then i reconnected it to the car harness, and noticed something strange:
- When temperature **** is in the coolest position, valve is closed.
- When i move the temperature **** by just one notch from coldest position (i counted 19 notches between coldest to hotest), the valve fully opens ?
- When i cut off the ignition, the ccu was "pulsing" the servo valve.

Any ideas?

ToreB

Since there is movement with ignition off, I suspect you have a CCU fault.
Cheers,
Tore

ble2011

FWIW, on my '95, I've just gotten used to the heat or air being on or off. Works great, either really hot or really cold, just no temp control. Its never bothered me as I never use the heat and when I needed the air, when it was 110 in UT, we never complained that it was too cold.

993c4ie

Thanks, Tore.
Will the "root cause" of the fault show up with the ScanTool? i am currently building an OBD serial adaptor...just missing a PNP transistor, and then should be good to go..

ToreB

Yes, failing servos will cause the Climate Control Unit to produce a fault code, readable by a Porsche compatible diag tool such as Scantool.
Cheers,
Tore

pp000830

If one put a low ohm resister in series with the motor it may forestall a wisher fry failure. Just enough resistance to lower the maximum current draw through whiskers while still providing enough power to the motor to run? Measure the resistance through the motor and add a resister of about half the measured ohm resistance as a starting point and run an electrical test. Also there is a place that rebuilds servos for about $200 +/1. Send your's in as a core and they rebuild it.
http://www.partisan-autoteile.de/epa...324%2000-AT%22

ToreB

The root cause in this is a failing motor, with a short circuit as result. You could of course install fuses or other stuff in series with the motor to avoid damage to the end switch circuits. However, you will have to change the servo anyway.
PARTisan servo exchange service is recommended.
Cheers,
Tore

993c4ie

I opened up an electric flap servo to take dc motor out. Motor is made by Johnson Electric.
Would anybody know the spec of this DC motor or of any compatible replacement?

Twood

On mine it was the potentiometer that had worn out-the motors seemed fine. I have a couple of motors in failed servos but I am a bit far away.
I would think there must be quite a few failed servos with okay motors but failed potentiometer

993c4ie

Thanks, Twood.
I would not think these motors were especially made for Porsche and they are made by truck loads in China...so i would have hoped relatively easy to locate.

Here is the link to the manufacturer page http://www.johnsonelectric.com/en/pr...tive-dc-motors

I think Tore had published somewhere that the stall current was around 450mA.

I would just like to know the no load speed of required motor?

Foxman

I took my C4 to the shop last week to check for fault codes. None were detected, but I'm not sure they were able to get a full read. The A/C was just recharged. A/C starts out fine for a few seconds, but then a whine ensues from the dashboard and the fan power cuts down to a minimum. All fuses check out fine. After reading Tore's thread here and connected links it sounds like the CCU fan may be failing. Question is can the CCU fan cause the A/C fan to cut out, or is it the entire CCU unit as shop suspects? Has anyone experienced these symptoms, and can a failing CCU fan cut the fan power? Thanks in advance for any feedback.