hullstate

955 has a croaking noise in the dash caused by the defroster vent servo continuously moving back and forth.. It will stop if I press the center vent button on the controls. The servos are $200 each, so I don't want to simply throw parts at it. Is there a way to verify that it's the servo and not whatever controls it? I can supply 12v power to the servo in question and it moves just fine.

slavie

It's not the servo moving part that is the problem, rather the servo feedback part that starts to get glitchy and reporting erratic signal. You can test it, but you need an oscilloscope - hook up the scope and look for the output position signal. You want to see smooth lines, no spikes and no breaks.
Contacts inside the servo get dirty and start reporting bad signal, so the ECU is not able to determine the position of the servo an the whole thing fails.
Search around - there was a video of a guy testing it with a scope, and comparing the earlier and the later revisions of the servo.

hullstate

Thanks for the response. Electronics repair is probably a little out of my league. Sounds like it's going to be new servo(s). Anyone have any insight into reasonably priced servos?

slavie

Reasonably priced? What do you think this is, a Hyundai? Kidding, of course, but no - the VW/Audi ones cost about the same and there are no aftermarket offerings.
Some folks have had good luck purchasing the whole HVAC assembly from a wrecker off a later car with updated servos and scavenging the servos. Porsche changed a supplier at some point, so newer servos are more reliable. I don't remember what year they did that.

hullstate

Haha, Thanks again. Read some posts that were 3 years old and the replacements were $60 and now $200. Ouch if trying to replace all, because they are a **** to get to.

brett968

I think the switchover to the updated servos was either in the 2005 or 2006 model year. I did what Slavie mentioned to my 2004, I purchased the entire HVAC distribution box off a later model and swapped over the newer servo motors. If OP has the old servos, I'd recommend to go this route as the old servo motors are very problematic. If OP has the newer servo motors, I recommend that they clean the pot contacts using Deoxit or something similar. The hardest part of the job is getting the servo motors out. Cleaning the pot contacts is easy. BTW, I would recommend cleaning the pot contacts on any used servo motors as well to get things back to baseline.