Triode Pete

Since I purchased my 1991 C4 Cab last December, I've had climate control problems as described below;

1) Constant heat from driver's side & defrost vents. Far right passenger's side & defrost vents blow cool air.
2) Round thermostat dial (blue & red dots) does not change temperature settings but in the ignition accessory position, the rear blower fan will turn on & off as the thermostat dial is rotated.
3) Upper & lower slide controls do not appear to work. There is no control of air distribution.
4) Variable Blower fan 0 to 4 does work properly.
5) Defrost button engages & blasts air when activated.
6) A/C button turns on (yellow light) but the condenser/compressor appears not to engage -- no change in RPM's, etc.

I had the local Porsche dealership troubleshoot the problem and they changed two servos. Still does not work! They said that they can't get power to the servos & that the CCU (P/N- 964 659 047 01 or new 993 659 047 00) must be faulty & should be replaced. I asked if they used the Bosch Hammer to diagnose --- they said "no" but they used something similar!!

To add insult to injury, they scratched my fenders & "dinged" my door!!! I guess it's time to go to an independent shop with Bosch Hammer tools!

Any ideas from anyone???

Thanks,
Frustrated Pete

burgass

Welcome to the club of "satisfied customers of local Porsche dealerships"!!!
I had the same problems withh the CCU and I had to change it. Before you do that check the small fan on the back of the CCU Sometimes it seezes to function and the unit starts acting crazy. There are 2 companiies ( USA and Italy ) that repair CCUs for a cost which is a fraction of what you pay for a neww one
Regadrs

Triode Pete

I believe the little fan on the back of the CCU works. I think I hear it running after I shut down the motor. I guess it may run for ~ 10 minutes after the ignition key is removed.

Thanks,
Pete

springer3

The hammer does an excellent job troubleshooting the climate control. I had 5 error codes on my system. It was still functional, but did not seem to cool as well as it should. All 5 codes were valid. One was for seized condenser fan motor - the one in the front left fender. Fixing the problems really improved the performance, particulary in cooling mode.

One of the codes was for inop fan on the back of the CCU module. The car had been sitting for a long time, and the rotor was just a little sticky. I got it moving, and the code did not come back. I am surprised the dealer does not give you a clear diagnosis.

Be sure to troubleshoot all the system components before swapping out the CCU. You can damage a brand new CCU if you connect it to certain failed components. CCUs are sometimes very easy to fix if you know how to replace components. Open the module, and scan the board for "crispy critters". I have gotten lucky, and been able to spot an overheated component that failed because it was connected to a seized motor. The logic components are difficult to diagnose and repair, but they seldom fail. I have always been able to find simple failures that were easy to fix.

Also look for cold solder joints - a common problem on German automotive electronics. It sometimes takes a keen eye to spot one. Use a magnifying glass. Any joint that is not uniformly glossy should be resoldered.

burgass

Do a search on the forum about the CCU. You will find the links to the companies that repair the unit.
I would check the car with a Hammer also. In case your CCU is faulty and you look for a spare send me a PM -I have a working unit that is OK
Regards

Triode Pete

Guys,
No error codes were registering & no signals could be read from the CCU through the Hammer.

I found a used CCU from a 1994 Turbo & it cured the problems, finally!!!! With Spring here, I don't have to suffer with constant heat!!!!!!!!!!

Thanks for the advice & support,
Pete

PS - Anyone need a defective P/N- 964 659 047 00 CCU? Yeah, an "00" P/N was installed in my 1991 C-4. Adrian Streather thinks it was installed in my 1991 model by mistake.

Colin 90 C2

If you're looking to get rid of the CCU, I'd love to take it apart to see what makes it tick (or not tick in your case)

Of course, I'd pay for any shipping costs.

Randall G.

My '91 had 964-659-047-00, too. As did a friend's. I'm guessing Porsche installed 'em until they ran out of stock.