Wow, these issues are driving me crazy as it seems there can be so many potential problems so find the solution is difficult unless someone has the exact same problem and has already figured it out.

Okay, All fans ans servos appear to be working. The fan is on 4 and I have directed the air to the center vents. It will blow hard for a few seconds and then without a change in fan speed very little air comes out. it's like a flap valve or something is blocking the air that the fan is trying to move to the vents. The air will then erratically without any good reason increase in force for a few seconds and then change back to almost nothing. one more thing, going over a pot hole or very bump road will also make the air come out strong for a bit and then it will once again go back to almost nothing until i hit another bump.

So where do I start? has anyone solved this problem?

Thank you

Peter

 

low on ac freon

 

If this happens with no change in fan speed, and the servos are working as they should, it may be that a flapper connecting rod came loose from its ball.

Mine does this too. I blame it on a bad pot for the fan speed control on the CCU. This could be the culprit for both issues, and there really may be a change in the fan speed (for problem #1).

 

Where would i find the Flapper connecting rod to check this?
A bad Pot? what do you mean and how do i check / fix this?

Thanks

 

Peter,
If I'm not mistaken, there is a right and left fan. When the air "slows down" from the center vents, it's either the fans slowing or an obstruction. I guess its feasible that the two center air flow tubes have something in them. However, it is more likely the fans, or fan, are actually slowing down. I would first remove the center vents and try to determine if the tubes are intack. My next thought would be to ensure the rods are adjusted and the servos are working properly. My last item would be the CCU.
You can check for physical issues pretty easily. Beyond that, you may be better off plugging a hammer in and capturing the codes.
I could be way off base on all this... there are far smarter people on this board than me!

Gary

 

I am anxious to hear a solution - I have the same issue. The volume of air exiting the vents is almost constant for the first 3 fan settings, with an obvious audible increase in fans speeds as I turn the ****. On 4 it seems that something opens up and finally allows air to flow - a LOT of it. Now, I know I have a problem with the left fan that has something in it that makes a noise at high rpm. But, I don't think this is the entire problem. My thought is that the fresh air flap is a player in this issue. When I test all the servos with the Scantool, they all respond open/close properly, including the fresh air flap.

 

You may have already been here, but this site should help with some of your questions and troubleshooting steps.

http://www.porsche964.co.uk/technical/servos.htm

I meant the fan speed control ****. It may not actually be a potentiometer, but it may be going bad and causing the intermittent issue. I've been told that this symptom may instead be a result of a bad final stage regulator but I need to search this forum to learn more about it.

https://rennlist.com/forums/7601794-post10.html

Here are a few links I found on my initial search.

https://rennlist.com/forums/964-foru...amplifier.html
https://rennlist.com/forums/964-foru...fan-speed.html
https://rennlist.com/forums/964-foru...ng-anyone.html

See also any embedded links and references to Loren and Otto for places to test and repair your CCU (if needed).

 

Mike
Thanks for the homework. Ha, really its very much appreciated. I will read anything I can get my hands on to solve this problem(s). I spoke with one Porsche dealer who mentioned something about flappers not working properly and problems with the differential pressures inside the system. I don't understand but perhaps someone else does and can explain in terms that we can use to investigate using our sweet equity.
Thanks again

 

Hey Mike,
Good info... I'm trying to learn as much about these systems as I can. Right now, I just finished cleaning the two air temp servos and adjusting the flapper rods. That seems to have resolved the constant warm air we were experiencing.
Peter, keep us informed on your progress.

Gary

 

Gary
yes, will do and please let me know if you resolve the lack of/intermittent air issue at the center vents.
Peter

 

I think the problem may be inside the CCU unit. The ribbon connector between the front panel and the main pcb may be dirty. Try unplugging it and spraying some contact cleaner on it then reassemble it. You can find instructions on how to get the CCU open here :http://privat.bluezone.no/toreb2000/ccurepair.html

 

mine will drop airflow but not fan speed when going from a cold to hot setting. I think despite the pusher fan on the engine (the rear blower) that there is alot of resistance in all that piping from the very rear of the car all the way to the front, and i'm sure the flapper valves in the rear wheel wells don't help either.

either that or there are mice living in those nice warm tubes...

 

The CCU is most probably NOT the issue here.
This behaviour is typical for inert or damaged fresh air or mixing servos. Or both.I'll try to explain:
I would suspect you are a bit up on the temperature setting by this time of the year. Most probably so high that the CCU closes the fresh air intake and try to open both mixing flaps (opens for heated air from the engine)
If these flaps are damaged they will probably be inert, in your case in the shut position. One or both. If so, you'll notice difference in air flow on left and right side of the dashboard.

When this is happening you'll get air in your face while the fresh air flap is open and closing. When it's fully closed the fans will have nowhere to draw air from since the mixing flaps are stuck in closed position. Therefore the sudden drop in air flow.

You will see the same behaviour coming from hot to cold temp setting with a damaged fresh air valve. You'll get air as long as the mixing flaps are open, once they are closed all air is supposed to be drawn from the closed fresh air intake.

The fan speed is involved in this too, as the CCU probably regulate the air temp depending on fan speed/air volume. A higher air flow will require more heated air to hold the same temperature.

I'll bet you get plenty of air if you press the resirc button. Then the resirc flap will open and air can be drawn from the cabin. You should hear a swooshing sound when it opens and get nearly full air flow. (if not, you probably also have a vaccum leak, making the resirc flap inert too)

The erratic behaviour of defective air flow control servos is typical. The whiskers in the position feedback potentiometer inside are burnt or worn, a whack or hitting a bump will maybe get it working temporarily.
Another example of the same is when you hear static noise when turning the volume **** on old stereos, that is caused by worn potentiometer whiskers or resistor tracks. The only remedy is to change the damaged servo(s). Beware, they are not cheap!

It's easy to verify the mixing valve operation: Open the kick panels in both footwells and see if the servos are moving when turning the temperature **** from cold to hot. They should close and open simultaneously. You may have problems spotting the movement of the flaps without detaching them from the air hoses.
You could also use a OBD tool to read out the fault codes from the CCU, you would then identify all faults without doing any work on the car.
My website expalins the details of the CCU and air system:
www.ccu.tore.bergvill.com

Oh, by the way, check the operation of all servos while you do this, especially the fresh air servo, it's moving a lot. This and the rest of the servos are placed under the windscreen.

Cheers,
Tore