LA964RS

I went through and read what threads I could find on this subject and this scenario sounds different than the ones I found.

My buddies '92 had the battery go dead recently...first time ever. Then he had the car kick a CEL. I went over to check it out and I reset the CEL and it didn't go back on when car restarted...but seems like the little fan motor in the CCU was just running....with the ignition off, key out! I'm like what's that noise...and it smelled like...you know that smell before smokes starts coming out of the dash?...Yeah, like that!

Anyway, pulled the battery neg again and let it sit for a bit. Hooked battery back up and no fan running....

So is this the sign that the v.expensive CCU is about to take a sh*t????

All the other functions of the CCU work fine....car is what 15 years old now...how long these units supposed to last?

Thanks.

Megatron-UK

Doesn't the fan run on for a bit when you switch off anyway? I'm sure I read that on here somewhere...

John52

There are a lot of documented problems with the CCU fan. I can only share my experience. Yes, the fan is supposed to stay running for 15 to 30 seconds after the ignition is shut off. However, in my case, it just kept on running until it killed the battery after a few days. All other CCU functions worked fine.

Given the price of a new CCU (big bucks) my mechanic opted to install a simple relay switch between the ignition and the CCU. When the ignition is on, power is provided to the CCU, when ignition off , no power to the unit , so the fan doesn't run.

dfinnegan

That fan will run for up to 20 mins after shutting the car off. Come back after 20 mins and if it's still running then there is a problem.

LA964RS

20 minutes! I've had a 964 for 7 years now and its never run that long....wonder if mine is working?

I think my buddy needs the fan issue resolved as I bet that's what drained his battery...

All great info, thanks.

JasonAndreas

If the fan is staying on for longer than 20 minutes and draining the battery the proper fix is to replace the transistor (T1) BC337 ($0.36USD) on the lower PCB. Unfortunately I don't know of any method to test the transistor without first removing it? Anyone here an EE?



Wick up the solder


Remove the component and clean the PCB with denatured alcohol


and don't use this much solder. and then clean again after its cooled.


I had to temporarily remove the component next to the transistor to place it properly. My only other option was to split the two circuit boards and that involves soldering a bunch of joints versus only two.

Laurence Gibbs

sorry to revive this old thread but........ has anyone else done this? what was the failure mode of the BC337 did it show up when tested with a meter?
I 've just torn mine apart and my BC337 tested fine. I have fitted a new one just in case it fails when livened up .
Any other possible reasons for the fan to stay on if it's not T1 ?

ToreB

Hi Laurence, I've done this fix several times and have not seen any cases of no shutdown without a defective transistor. I've seen one note on your problem though, but have not been able to verify this, nor the cause.
I can help you diagnose your CCU if necessary.
Cheers,
Tore

Lorenfb

Replacement of the mentioned device doesn't usually solve the problem.
The CCU ECU is intermittent requiring repair/rebuilding. Read here under
'Porsche CCU964/993':
http://www.systemsc.com/problems.htm

STUARTQ

Sorry to restart yet again, but I have a CCU issue.
My CCU works very intermittently.
I switch it on and nothing happens, no blower, no matter where the temp control **** is turned or which buttons are pressed or where the sliders are set.
Then as I drive along, it will start blowing, sometimes for several minutes, mostly for just a few seconds, then switches off.
I've read through various threads inc Tores very useful info, but confused as to what the problem is.

garrett1021

I have a similar problem, except.....

My ccu has never ever worked... except one fateful night about 6 months ago.

For about an hour, my ccu worked, and my spoiler would go up and down (normally I have it in the fixed up position because it doesn't work)

That was the most glorious hour of my life... then everything just stopped all the sudden. No idea what happened

ToreB

stuartq, it seems that you have problems with the front blower operation. When you write "switch it on" I interpret that to mean that you turn up the fan speed button. Does the other HVAC functions work normally? If so, you probably have nothing wrong with the CCU itself.

You might have a problem with the rear fan, this will cause problems. You also might have problems with the fan amplifier stage, located behind the fuse box. You could do the HVAC DIY test mentioned on my web page to find any faults.
Cheers,
Tore

STUARTQ

Thanks Tore, I was hoping you might see this.
I'll try the HVAC DIY and go from there.
My car is a non A/C, I'm considering the rear fan delete too, so will start as you have suggested.
Thanks for your answer.

LM964

I replaced my rear fan motor with a brand new one last year (the old one had shaft bearing failure and was ruining the fan and shroud).

However, I know my non-A/C CCU now needs a service/repair job as nothing works properly on it (or is extremely intermittent - some life for 5 seconds then nothing). Rear fan never comes on - I know it works fine as I've spun it up in situ.

So, still on my to do list and will worry no more about it until I send it off... The 964 HVAC is such a pain in the **** to fathom out..

JasonAndreas

What happens if you start the car with the CCU controls set to MAX TEMP and MAX speed?