BlackCab

I have a problem with a fan running continuously unless I pull Fuse #1 for the A/C. That's the only way to stop the fan from running. When it's running, air is not flowing through the vents, but you can hear the fan loudly from behind the dash. I have read some great threads and seen sites on removing the CCU. I'm ready to proceed with this if necessary but in the back of my mind I'm thinking what if it's not the CCU? Does anyone know of anyway to test the CCU or do these symptoms point unequivocally to it? Thanks...

Adrian

Yep you pull out the ccu, remove the little fan at the back of it and plug the ccu back in. If the noise and constantly running fan has stopped you have found the problem. You can leave the fan off. This does not fix the problem but it stops the annoying noise and possible flat batteries. Previous experience shows that this sensor fan has no impact on the normal running of the cooling or heating system if it is removed.
I am assuming that you have not got the temp control **** in the heating range (out of blue dot position) and you waited 20 minutes to allow the fan to turn off.
Ciao,
Adrian
964C4

BlackCab

You would be correct on both assumptions.
So you're saying I can permanently remove that fan without resultant A/C or heat problems? Can you buy a replacement temp sensor and fan or would you have to get a whole new CCU?
I listened by the passenger front tire after I read that the CCU also controls the oil cooling fan but you can't hear anything. You can only hear the fan from inside the car by the CCU.

BlackCab

well, now that I'm reading inside the fuse box lid, fuse #1 only controls the blower inside the compartment which sounds like the fan you're referring to. That sounds like that would support the idea that removing that fan/sensor assembly would stop the symptoms. Thanks!

BlackCab

Last but not least (well, I shouldn't be promising things) is there a driver transistor that fails that, in turn, causes the CCU fan to run continuously? Or, is there an upstream transitor or IC that fails and this failure causes the driver to remain on? I'm trying to figure out if the problem lies within the CCU itself or are components outside of the CCU involved?

Randall G.

Hey BlackCab,

You need to make an important distinction here. Is it the little fan that's connected to the back of the CCU that continues to run, or one of the "interior" fans in the trunk (left and right side)?

You should be able to put your head beneath the dash (under the CCU) to determine if it's the CCU-attached fan that's running. As Adrian has already pointed out, it's normal for this fan to run awhile after the ignition is turned off.

If it's one of the interior fans that continues to run, good chance you have a failed final stage regulator (FSR). Which is basically a variable resistor between the fan (and its 12V power) and ground, which controls the left & right fan speeds. (You had the right idea about an IC in the fan power circuit.)

The interior fans are also powered by fuse #1.

The FSR is in the same area as all of the servo motors, under the flimsy plastic cover, near the center. It looks like this, when removed from the car:

http://members.rennlist.com/rgranaas...%20Circuit.JPG
http://members.rennlist.com/rgranaas/Regulator1.JPG

Hope this helps, and good luck!

Adrian

If its the temp sensor fan the failure is inside the CCU. You can get them repaired.
Fuse No 1 supplies the power to the entire system not just not just the blower fan(s). There are 3 fans under the control of that one fuse. The ccu itself controls the operation of 6 fans.
To understand all the componets of the system I suggest you purchase my book on the 964. This is all covered in some detail.
Ciao,
Adrian
964C4

BlackCab

I do have your book and was reading the part about the CCU earlier today. I have to look through it more tonight to find out about these other fans. When I put my head right by the CCU that seems to be the best place to hear the fan running. It's sort of loud to be coming from such a small fan. I will try to just pull it out and disconnect the fan to see if that solves it. I really appreciate the pictures of the FSR. That will be my next approach. I really appreciate it...

Lorenfb

The problem you describe is a common CCU failure mode which results in excessive
current drain on the battery, i.e. usually over 100ma drain. This excessive drain causes
the battery to fail after a days without driving or externally charging the battery.
A normal battery drain/draw should be < 60 - 70 ma.

Disconnecting the fan reduces the excessive drain but doesn't totally solve the
problem. The CCU still remains "on" causing an additional battery drain above
normal.

Bottomline: A new CCU or a rebuilt unit.

BlackCab

Man, I just took the CCU out, disconnected the fan, put the CCU back in, and then plugged fuse #1 in. The good news is, I no longer heard the fan in the middle of the dash by the CCU. The bad news is, cold air is coming out of both side vents. Bummer! The key is out. The CCU is off.
Then out of curiosity I plugged the fan back in, but the side vents are blowing still. The fan sound is still louder and distinctly coming from the sides if you stick your head under the hood.
What in the world? Loren, does this go along with what you're saying? The CCU is bad and it's manifesting in these different symptoms?

Randall G.

This sounds like your final stage regulator (FSR)--see my post above. It's supposed to "open" the fan circuit when the ignition is turned off. Obviously, your fans (in the trunk) still have a completed circuit (or else they wouldn't be running).

It could still be your CCU, however (CCU is sending signal to run the fan, even though the ignition is off). Before purchasing a new FSR, I would recommend installing a friend's CCU, long enough to verify the problem is still present.

Good luck, and let us know what you find.

Lorenfb

The final stage fan controller acts as an electronic resistor to vary the the blower
fan speed. Its input (0 to 12 volts) comes from the CCU. If the you disconnect the
CCU and the fans continue to run whether the key is "on" or "off", then the fan
controller is bad. The fans receive #30 power and are grounded, i.e. electronically,
by the fan controller.

BlackCab

The fans are still running and the CCU is sitting on the kitchen sink. Sound like a reasonable vote for the FSR?
BTW, what do you mean by #30 power?
And the other thing is--now that I'm looking inside the CCU. Behind the 4 Siemens ICs (behind IC9), there looks to be an electrolytic capacitor with some white dried goop looking stuff around the bottom. Did this possibly leak from the capicitor? ie, does anyone think there could be multiple problems here? Or is that how they normally appear?

BlackCab

This picture shows some of the capacitor behind the 4 IC's. you can see the white substance in question at its base. Anyone seen that before?

Lorenfb

The "stuff" is used to keep the large component from vibrating and breaking lose.
Avoid "playing around" inside the CCU unless you're a knowledgeable electronics
type or you may really cause a fault or make the unit non-reparable. You're generally
not going to "see" the problem in most electronic unit failures.