ccu rebuild
08-01-2003, 11:42 PM
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ccu rebuild
Spoke to "OTTO" of "ottos of Venice (California) today about repairing the ccu from my '91 C2. He said he had a good electronic repair guy that works on all types of electronic devices from various years Porsches. Thought a ccu would take only one day turn around. I'll keep the list posted on my success.
08-02-2003, 02:00 AM
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Hey Jerry,
If you make it out to the coast, you're welcome to try my spare CCU long enough to see if it fixes your problem, before $springing$ for a rebuild. The unit works fine, with the exception of (not) starting the oil cooler fan automatically.
If you make it out to the coast, you're welcome to try my spare CCU long enough to see if it fixes your problem, before $springing$ for a rebuild. The unit works fine, with the exception of (not) starting the oil cooler fan automatically.
08-02-2003, 02:39 AM
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Randall
Hmmmm. My wife has just been laid up with a hip replacement. She's getting along fine at the present, but I may have to spring out of here to regain my sanity. My son lives in the LA area, and I just might take you up on your offer, and visit his family in the mix of things. If the ccu proves to be bad, which I suspect, I could drop than it off with "Otto." It would also let you see a 964 with a 964 drivetrain (tongue in cheek.) When would be the best time for you? Incidently, several of my 356talknet buddies know "Otto" ., nom de guerre, and describe him as a good wrench, with a good shop, and a racing fanatic.
Hmmmm. My wife has just been laid up with a hip replacement. She's getting along fine at the present, but I may have to spring out of here to regain my sanity. My son lives in the LA area, and I just might take you up on your offer, and visit his family in the mix of things. If the ccu proves to be bad, which I suspect, I could drop than it off with "Otto." It would also let you see a 964 with a 964 drivetrain (tongue in cheek.) When would be the best time for you? Incidently, several of my 356talknet buddies know "Otto" ., nom de guerre, and describe him as a good wrench, with a good shop, and a racing fanatic.
08-02-2003, 10:54 AM
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Hey Jerry,
Sunday mornings are usually good for me these days. Or, later in the afternoon on Saturdays. Been working a lot of Saturdays lately--like today.
Sunday mornings are usually good for me these days. Or, later in the afternoon on Saturdays. Been working a lot of Saturdays lately--like today.
08-02-2003, 12:58 PM
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Randall
Now I'm feeling REALLY dumb. For the past year I was under the mistaken impression that the variable speed switch on the face of the CCU (reads 0,1,2,3,4) was to activate the rear blower fan. When I iinstalled the new rear blower fan, and the switch still didn't do anything, I started re-reading all the old posts and carefully going over the factory manual and wiring diagrams on the subject. Roly mentioned that the variable switch, if I read him right, activated the left hand blower only. Is this right? Or just what on earth does that variable speed switch attach to/control? Next question, is the rear blower fan only activated by temperature? If so, just how?When the rear blower fan is operating, where does its produced air go, i.e. just what is it's purpose? When I manually jump the rear blower fan I feel no breeze inside the car. ARGHHH!!! Wife is beginning to think that I'm not as smart as my EE degree sez. Am I asking too many questions?
Now I'm feeling REALLY dumb. For the past year I was under the mistaken impression that the variable speed switch on the face of the CCU (reads 0,1,2,3,4) was to activate the rear blower fan. When I iinstalled the new rear blower fan, and the switch still didn't do anything, I started re-reading all the old posts and carefully going over the factory manual and wiring diagrams on the subject. Roly mentioned that the variable switch, if I read him right, activated the left hand blower only. Is this right? Or just what on earth does that variable speed switch attach to/control? Next question, is the rear blower fan only activated by temperature? If so, just how?When the rear blower fan is operating, where does its produced air go, i.e. just what is it's purpose? When I manually jump the rear blower fan I feel no breeze inside the car. ARGHHH!!! Wife is beginning to think that I'm not as smart as my EE degree sez. Am I asking too many questions?
08-02-2003, 01:30 PM
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Hey Jerry,
It is pretty confusing after all. So, no need to be too hard on yourself.
The rear blower has a heating function and an engine cooling function.
In the heating mode:
-The rear blower is started in slow-speed when the temperature control **** is taken to ~21C or greater. That is, it starts to supply heated air to the cabin.
-The rear blower sends air through the left/right heat exchangers. This air is in turn mixed with fresh air at the left/right interior fans.
-The speed of the left/right interior fans in the trunk are controlled by the **** on the CCU (variable speed switch, as you call it).
-I've also read/heard that one of the fans in the trunk is for the "interior fan," the other is for the defroster. But, based on the way the system is designed, I don't see how this can be true. I think both fans are on all the time, considering how air is mixed on the left and right sides of the system. If only one fan runs, how does air get mixed on the other side?
-If you are requesting heat in the interior (>21C), and turn the interior fan **** to ~>2, it will cause the rear blower to run in fast-speed.
Now, for the rear blower engine cooling mode:
-Ignition off, the rear blower will start at 75C at the rear blower temperature sensor, off at 70C.
-Ignition on, temperature mixing flaps closed (heat not requested in cabin), rear blower operates in engine cooling mode:
*Rear blower starts in slow-speed at 45C, off at 40C.
*Rear blower starts in fast-speed at 62C, off at 57C.
The above explains why you sometimes hear your rear blower start-up when you take the key to the ignition position, getting ready to restart the engine shortly after turning off, temperature control **** at blue-dot.
This is a mouthful, but I think it will start making sense for you.
Oh, and with respect to your jumpering the rear blower and not feeling any breeze in the car. Of course, you won't feel anything if the mixing flaps have closed off the hot air supply.
It is pretty confusing after all. So, no need to be too hard on yourself.
The rear blower has a heating function and an engine cooling function.
In the heating mode:
-The rear blower is started in slow-speed when the temperature control **** is taken to ~21C or greater. That is, it starts to supply heated air to the cabin.
-The rear blower sends air through the left/right heat exchangers. This air is in turn mixed with fresh air at the left/right interior fans.
-The speed of the left/right interior fans in the trunk are controlled by the **** on the CCU (variable speed switch, as you call it).
-I've also read/heard that one of the fans in the trunk is for the "interior fan," the other is for the defroster. But, based on the way the system is designed, I don't see how this can be true. I think both fans are on all the time, considering how air is mixed on the left and right sides of the system. If only one fan runs, how does air get mixed on the other side?
-If you are requesting heat in the interior (>21C), and turn the interior fan **** to ~>2, it will cause the rear blower to run in fast-speed.
Now, for the rear blower engine cooling mode:
-Ignition off, the rear blower will start at 75C at the rear blower temperature sensor, off at 70C.
-Ignition on, temperature mixing flaps closed (heat not requested in cabin), rear blower operates in engine cooling mode:
*Rear blower starts in slow-speed at 45C, off at 40C.
*Rear blower starts in fast-speed at 62C, off at 57C.
The above explains why you sometimes hear your rear blower start-up when you take the key to the ignition position, getting ready to restart the engine shortly after turning off, temperature control **** at blue-dot.
This is a mouthful, but I think it will start making sense for you.
Oh, and with respect to your jumpering the rear blower and not feeling any breeze in the car. Of course, you won't feel anything if the mixing flaps have closed off the hot air supply.
08-02-2003, 07:38 PM
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Randall
Ohkaaayy. So if things are working correctly, the multi-speed switch on the CCU controls the speeds on which fan(s), other than the rear fan at or above 21C? But that rear fan only has two modes, other than off. Why does the interior switch have 5 settings?
Where, physically, are the mixing flaps? If they are shut off, can I manually open them without buggering the whole system?
Ohkaaayy. So if things are working correctly, the multi-speed switch on the CCU controls the speeds on which fan(s), other than the rear fan at or above 21C? But that rear fan only has two modes, other than off. Why does the interior switch have 5 settings?
Where, physically, are the mixing flaps? If they are shut off, can I manually open them without buggering the whole system?
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08-02-2003, 08:08 PM
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Hey Jerry,
The multi-speed switch on the CCU always controls the speed of the fans in the trunk--one each on the left and right.
The multi-speed switch on the CCU has discrete numbers, but it's really infinitely variable speed control. That is, it doesn't just have speeds 1, 2, 3, 4. It can be those speeds and anywhere in between. It uses what's called the "blower final stage" to achieve the infinite speed control. Basically, a glorified rheostat (as an EE, that's a concept you can get your arms around ).
When the multi-speed switch (interior fan control ****) on the CCU is turned past 2, and heat is requested in the cabin, it will also cause the 2-discrete speeds rear blower to switch to fast-speed, to supply additional heated air. The only difference between slow and fast-speed for the rear blower is a resistor between the 12V power supply and motor (another concept you can get your EE arms around ).
Adrian gave you an idea of how to manually manipulate the flaps in another thread.
Try reading what I wrote above in my previous post a few times. I think it will start making sense on the third or forth (slow) read.
Bring your car here, bet we'll either have it fixed or know what's ailing it in 2 hours or less.
The multi-speed switch on the CCU always controls the speed of the fans in the trunk--one each on the left and right.
The multi-speed switch on the CCU has discrete numbers, but it's really infinitely variable speed control. That is, it doesn't just have speeds 1, 2, 3, 4. It can be those speeds and anywhere in between. It uses what's called the "blower final stage" to achieve the infinite speed control. Basically, a glorified rheostat (as an EE, that's a concept you can get your arms around
). When the multi-speed switch (interior fan control ****) on the CCU is turned past 2, and heat is requested in the cabin, it will also cause the 2-discrete speeds rear blower to switch to fast-speed, to supply additional heated air. The only difference between slow and fast-speed for the rear blower is a resistor between the 12V power supply and motor (another concept you can get your EE arms around
). Adrian gave you an idea of how to manually manipulate the flaps in another thread.
Try reading what I wrote above in my previous post a few times. I think it will start making sense on the third or forth (slow) read.
Bring your car here, bet we'll either have it fixed or know what's ailing it in 2 hours or less.
08-02-2003, 11:46 PM
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Randall
Thanks for the details. I've got it. One of the problems that I think I have is with the multi-speed switch on the CCU. It has three pins on its back connecting it to the circuit boards. I previously measured the resistance between the three pins, at various setting positions, and get the similar readings between the pins at psn 1, 2, and 3. Only at psns 0 and 4 do I get differences. If it either acts as with a continues variable resistor, or as a 5 way switch, it appears messed up. I'm going to carefully mull over the past notes and hopefully have much more success than I've had over the past months. Realistically, I'll probably see you soon!
Thanks for the details. I've got it. One of the problems that I think I have is with the multi-speed switch on the CCU. It has three pins on its back connecting it to the circuit boards. I previously measured the resistance between the three pins, at various setting positions, and get the similar readings between the pins at psn 1, 2, and 3. Only at psns 0 and 4 do I get differences. If it either acts as with a continues variable resistor, or as a 5 way switch, it appears messed up. I'm going to carefully mull over the past notes and hopefully have much more success than I've had over the past months. Realistically, I'll probably see you soon!
08-03-2003, 03:14 AM
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Hey Gerry,
The "blower final stage" is located external to the CCU, beneath the black plastic cover, with the rest of the servos, etc. 12V from both the left/right interior fans go into the final stage, the final stage is between the interior fan power and ground. That is, the final stage completes the interior fan circuit, and in the process determines how much current (proportional to fan speed) to pass through the fan motors.
Pins #G31 (right hand blower) and #G34 (left hand blower) of the CCU are the control signals to the final stage.
If the CCU fan speed control **** operates like the servo motor position sensors:
-One pin is for +5V.
-One pin is ground.
-The 5V is across a fixed resistor.
-The third pin is for a pick-up that moves across the resistor as the servo (****) moves.
-The voltage on the third pin is proportional to position. On one extreme end of the resistor, the reading is 0V. On the other end, the reading is 5V.
The "blower final stage" is located external to the CCU, beneath the black plastic cover, with the rest of the servos, etc. 12V from both the left/right interior fans go into the final stage, the final stage is between the interior fan power and ground. That is, the final stage completes the interior fan circuit, and in the process determines how much current (proportional to fan speed) to pass through the fan motors.
Pins #G31 (right hand blower) and #G34 (left hand blower) of the CCU are the control signals to the final stage.
If the CCU fan speed control **** operates like the servo motor position sensors:
-One pin is for +5V.
-One pin is ground.
-The 5V is across a fixed resistor.
-The third pin is for a pick-up that moves across the resistor as the servo (****) moves.
-The voltage on the third pin is proportional to position. On one extreme end of the resistor, the reading is 0V. On the other end, the reading is 5V.
