mojo747

The wiring had been messed with on the plug to this servo. Probably why it got fried. Anyone have the proper wiring format for the servo plug? The other servo appears unmolested. I'm curious what the deal is with that one.

mojo747

Yet another update. I scraped off the fingers on the fried servo and jumped the board with the 9v and it occurred to me that the servo only goes so far by design. I reversed polarity and it runs all the way back to the stop, reverse and it goes again. Seems to be functioning properly. I'll reinstall and see what happens.

jgrosjean

I have tried to fix the servos, and it is usually does not work. In one case, the motor was shorted. They are expensive, but a new one seems to be the best solution.
I had hot air all the time also and found that it was due to the foam rubber in the flaps being worn out. I replaced it with some soft silicone foam and fixed it. You will need to drill out the rivets in the flaps and replace them with screws. I did it with the heater out of the car, but it can be done in the car.

mojo747

I couldn't fix mine either. I reinstalled the passenger side servo and turned the key on, it cycled all the way in one direction and quit. Adjusting the CCU from hot to cold did nothing. I removed the driver's side servo and took it apart. Motor is good but can't get it to work through the motherboard. Funny since this one appears to be in much better shape inside. I tried hooking the passenger servo up to the driver's side plug but it still didn't work. At least while the servos are out I won't be cooking in the car. Alabama is hot man.

ToreB

Good to hear you found the fault. There's lots of those pictures of fried servos on this forum. I myself has also posted some. Maybe your shop guys need a look on Rennlist? :-)
Regards, Tore

mojo747

Thanks ToreB, Alfred and everyone. I appreciate your insight. I would still like to know the wiring sequence. If that is fine, I wonder if they were out of adjustment and got in a bind at fully closed or fully open.

ToreB

I think the circuit inside the servo is just a bad design. Maybe too much current through the resistive position sensor or a malfunction in the edge-stop mechanism. Anyway, a very common fault, and easy to detect if the air flap is stuck in the fully open position, thus the "whiff" of hot air in half of the dash vents.
Glad to be of any help mate.
Tore

mojorizing

For the right mixing servo:
pin 1 is green/ white
pin 2 is brown/ blue
pin 3 grey
pin 4 is yellow/ grey
pin 5 is blue/ grey

For the left:
pin 1 is green/ white
pin 2 is brown/ blue
pin 3 green
pin 4 is blue/ green
pin 5 is yellow/ green

It's possible that someone reassembled the arm on the servo output shaft at the wrong angle on the splines causing it not to stroke right.

mojo747

Thanks mojorizing!

mojo747

OK. Checked the pins in the plugs. Passenger was correct. Driver had pins 1 & 2 reversed. I switched them and hooked up the servo, it cycled all the way in one direction and stopped. I took the passenger servo and hooked it to the driver plug. It cycled all the way in one direction. Remember, they cycled all the way the other way when I hooked them on the pass side. So they seem to work in both directions.
I have a question. I'm only turning the ignition on to cycle these. Is it possible that they will only close without the engine being warm? Do they stay closed until the engine is warm enough to provide heat? I mean it is climate control right?

mojorizing

With the ignition key in , but engine not running, both servos should stroke as you turn the temp. **** from one extreme to the other. Do you have access to a scantool? You could cycle each servo separately with the software.

mojo747

No I don't. I was hoping you would tell me the car has to be warm.

mojorizing

To recap, you're confident that the operation of the servos tested on the bench, out of the car - they operate in both directions?

Here's my theory....

Finding that the feedback signal was *** backwards on one servo, the CCU kept giving the servo power and burned up the driver chip. Both servos have IC 11 in common, that's the chip behind the one in this picture....
That's from http://www.porsche964.co.uk/technical/climate.htm

What model # ccu do you have? 964 xxx or 993xxx?

mojo747

I'm not sure which one I have. The servos worked in both directions off a 9v if I reversed polarity. When both were hooked to the right side plug, they cycled fully in one direction, on the left side plug they cycled fully the other way. So your thinking my CCU has a fried chip?

mojorizing

When working, these servo's work in unison but in opposite directions due to the fact that the linkages are coming off at opposite angles. So a servo switched from one side will rotate opposite, as yours does. Does your CCU have only one button to turn on the A/C? or two half-sized buttons?