CCU Servo
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Joined: Apr 2004
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From: Oslo, Norway
pcarhombre, thanks for the feedback.
Maybe it's my language skills, but I don't fully understand what you have tested. If you get no heat from the rear the most probable reason is defective mixing servos.
The easy way to spot this is to remove the carpet covers in both footwells and watch for servo movement when cycling hot-cold-hot-cold on the temperature ****. The servos should open when temp is set to max, and close when set to minimum temp. If you have done this already the CCU can be the culprit. Since some of the other functions in the air flow system works I suspect no fault in fuses etc.
Maybe the temperature control element behind the **** in the CCU is damaged. Rare fault but possible. It's a normal potentiometer so it can be changed or cleaned. Use good quality electronics cleaning fluid with anti-corrosion properties. Do not use 556 or similar oily stuff.
Stealth 993 are right in mentioning a vacuum operated part, it's the resirc flap and only that. You don't need a pump to check operation of the flap, just suck on the line end if needed.
Cheers,
Tore
Maybe it's my language skills, but I don't fully understand what you have tested. If you get no heat from the rear the most probable reason is defective mixing servos.
The easy way to spot this is to remove the carpet covers in both footwells and watch for servo movement when cycling hot-cold-hot-cold on the temperature ****. The servos should open when temp is set to max, and close when set to minimum temp. If you have done this already the CCU can be the culprit. Since some of the other functions in the air flow system works I suspect no fault in fuses etc.
Maybe the temperature control element behind the **** in the CCU is damaged. Rare fault but possible. It's a normal potentiometer so it can be changed or cleaned. Use good quality electronics cleaning fluid with anti-corrosion properties. Do not use 556 or similar oily stuff.
Stealth 993 are right in mentioning a vacuum operated part, it's the resirc flap and only that. You don't need a pump to check operation of the flap, just suck on the line end if needed.
Cheers,
Tore
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From: Oslo, Norway
I agree Gordo, it sounds like a "ploooph". You also see the flap operate if you look up under the dash from beneath the steering wheel. Definetly sounds like you at least have a functioning resirculation flap mecanism. Whohoo!
Tore
Tore
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After a combined 8 hrs chasing this thing down, I stopped at my independents' today. He is going to scan the car tomorrow and see what the codes tell us. I'll keep you all posted and thanks for all the help & encouragement!
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Ok. Now I'm really stumped. I dropped by my guy today and the scan showed no faults for ac/heat! At this point, I'm leaning towards the memory that the rotary switch on the temperature **** might be shot (like Tore said). Prior to this complete fail, there were times when I had to "play" with the switch to get it to work and then use the fan speed to control the flow. Does anyone know where I can source a new one?
Since the servo in the footwell will turn when juiced by a battery, it might make sense that it is opening but the potentiometer is not calling for hear. Does this make sense or is it the case that if that flap is open heat will flow?
@Stealth: Is there a way I could stick my hand somewhere to see if hot air is flowing out of the fan in the rear? I KNOW it isn't getting up to the footwell b/c the tube is stone cold where it connects to the servo.
Oh yes: the GD airbag just lit up. Arrggh!
Since the servo in the footwell will turn when juiced by a battery, it might make sense that it is opening but the potentiometer is not calling for hear. Does this make sense or is it the case that if that flap is open heat will flow?
@Stealth: Is there a way I could stick my hand somewhere to see if hot air is flowing out of the fan in the rear? I KNOW it isn't getting up to the footwell b/c the tube is stone cold where it connects to the servo.
Oh yes: the GD airbag just lit up. Arrggh!
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Joined: Apr 2004
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From: Oslo, Norway
I would try clean the potentiometer for a fast fix, and then start searching for a defective CCU unit, or even only the front part. The pot spindles are a bit odd, and you might run into problems searching for a new one from an electronics supplier.
All defective servos I have seen have full functioning motors/gears but a defective/burnt internal feedback potentiometer. Therefore, connecting a battery directly to the motor pins on the servo will get it moving OK. But, the feedback signal to the CCU will not be there or indicate wrong position and the CCU will stop it due to emergency reasons.
Remember, both mixing servos shall move simultaneously.
I have always worked on cars with heated air ready at the servos, and sadly cannot help you with the fault in the engine compartment. However, I've seen notes on a faulty rear blower, that is mentioned on my web page.
Keep up the good work, I'm confident we'll solve this one mate.
Cheers,
Tore
All defective servos I have seen have full functioning motors/gears but a defective/burnt internal feedback potentiometer. Therefore, connecting a battery directly to the motor pins on the servo will get it moving OK. But, the feedback signal to the CCU will not be there or indicate wrong position and the CCU will stop it due to emergency reasons.
Remember, both mixing servos shall move simultaneously.
I have always worked on cars with heated air ready at the servos, and sadly cannot help you with the fault in the engine compartment. However, I've seen notes on a faulty rear blower, that is mentioned on my web page.
Keep up the good work, I'm confident we'll solve this one mate.
Cheers,
Tore
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I tried cleaning the pots when I first took the unit out. I'll try again but I was thinking: if I take the servo that is in the footwell off, should I expect the air coming out to be hot? And if it IS hot, does that point back to the CCU or the servo under the bonnet? Sorry if I'm bugging you all too much with all of this.
Burning Brakes
Joined: Sep 2006
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From: WetCoast, Canadä
I ended up having to order a refurbished unit from Porsche with the core exchange.
Even though the CCU is working great I did notice that the Footwell Servo (#3 on Tore's website picture) is not moving. I have taking it out and was wondering if I could check the function with a 9v battery and if so which of the poles numbered 1~5 (see attached picture) would need to be connected?
Are these Servo's rebuildable?
Even though the CCU is working great I did notice that the Footwell Servo (#3 on Tore's website picture) is not moving. I have taking it out and was wondering if I could check the function with a 9v battery and if so which of the poles numbered 1~5 (see attached picture) would need to be connected?
Are these Servo's rebuildable?
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Burning Brakes
Joined: Sep 2006
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From: WetCoast, Canadä
Will put it back in the car and check overall function from the refurbished CCU.
Thanks and good luck with your troubles.
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Today, we swapped out a fully functional CCU for mine and found that the problem still exists. What we did learn was that the servo on the driver's side (under the bonnet) is connected to a small rod that is in turn connected to a black rubber fitting and when the temperature **** is rotated from hot to cold, the arm has a hard time moving back and forth. Mostly, it seems to "skip" back to the closed/cold position. What I am now trying to understand is whether that servo and arm sends control information to the servo in the footwell, or if the footwell servo is fully controlled by the CCU. That would partially explain why the heat was not getting past the footwell servo. We are going to proceed with a troubleshooting session and hopefully determine further what the hell is going on.
The good thing is that by pushing the rod, I do have heat in the cockpit, and I can control it somewhat with the fan.
The good thing is that by pushing the rod, I do have heat in the cockpit, and I can control it somewhat with the fan.
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Joined: Apr 2004
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From: Oslo, Norway
What servo does not function pcarhombre? See the picture on my web site. I would think the internal potentiometer in the servo is damaged, erratic or no servo movement is typical for this type of fault.
You could connect another servo to the servo connector/harness in question to see if this moves OK. If so, you have found your fault.
By the way, the servos are not interconnected, but all move independently by CCU control.
Cheers,
Tore
You could connect another servo to the servo connector/harness in question to see if this moves OK. If so, you have found your fault.
By the way, the servos are not interconnected, but all move independently by CCU control.
Cheers,
Tore
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Tore: #3. That's the one that throws the little rod that brings heat. I think that must control both footwell valves b/c neither side responds to the CCU. Do you know what that rod is connected to? I was told the servos are all different. #3 has an arm connected to it. When I inspected the inside of the servos, I had to work around the arm b/c it would not come off. TIA
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From: Oslo, Norway
Servo number 3 is the one that controls the air flow to your feet. It does not control the amount of heated air from the engine. This servo is controlled by the lower slider on the CCU. It should not move when you adjust the temperature setting.
The two servos in the footwell sides control the amount of heated air from the engine and should open and close when adjusting the temp setting. They should move simultaneously. Are both these stationary, and the #3(footwell air flow) has erratic movement? I would then suspect all these servos are shot mate. I have changed three servos in my car, it is a common fault.
Cheers,
Tore
The two servos in the footwell sides control the amount of heated air from the engine and should open and close when adjusting the temp setting. They should move simultaneously. Are both these stationary, and the #3(footwell air flow) has erratic movement? I would then suspect all these servos are shot mate. I have changed three servos in my car, it is a common fault.
Cheers,
Tore