Subject: AC Ballast Resistor Replacement
Date: Thu, 27 Dec 2001 19:37:24 -0500
From: "Mike Feinstein" <mikncath@bellsouth.net>
To: "Randall Granaas" <rgranaas@flash.net>
Randall,
Thanks again for all your help with diagnosis, and encouragement with the repair. As you know, my oil cooler sending unit was the culprit and a new one solved that problem. Also, thanks to your directions for diagnosing fan problems, I was able to pinpoint the A/C ballast resistor as the problem in the other front fender. Besides having no low speed fan when using a jumper as you describe, when the AC system was turned on, the high speed fan would cycle on and off at 15 to 20 second increments...also a tell-tale sign that the ballast resistor is gone. Pulling the fender liner of my 94 964 confirmed this diagnosis. The old ballast resistor was literally missing a third of the ceramic material that holds it together. It is suspicious that
the batter overflow tube is located directly above the resistor. This explains alot. I'm amazed that Porsche would design it this way.
First thing I did was add a length of plastic tubing and attach it to the "spigot" that protudes through the inner fender wall to drain any battery overflow to the ground. Be sure to tie wrap the tube to ensure no interference with fan operation.
Under normal circumstances, the resistor is easy to reach and remove...there is an allen screw that attaches the resistor to the top of the condensor shroud and it threads into a nut that is welded in place on the inside (unreachable) of the shroud. The allen screw uses a 4mm allen wrench. Unfortunately, the allen screw on mine was rusted solid and the head broke
off when I attempted to unscrew it, leaving a permanent stud mounted to the top of my condensor shroud. I suspect that a bit of battery acid overflow caused this corrosion and ate my resistor at the same time. Suspisciously though, there is no other evidence of battery acid leakage...strange.
I started the car and turned on the AC with the new resistor plugged in, but unmounted....the AC fan came on low speed and stayed that way.......a beautiful thing. I agonized for some time about a suitable location to mount the new resistor. Since the resistor wire is fairly short, I decided to mount it to the inside fender wall, just above its original location (see pics). To do this, I had to drill a small hole in the fender wall to accomodate a single 6mmx30mm stainless hex head bolt. I placed a lock nut in the hex opening in the resistor (it was clearly made for this) fastened it in place with only the screw head and a washer showing under the front carpeting against the fender liner. Be careful not to over tighten the resistor because it appears to be made of a ceramic type of material and seems like it could break with too much torque on the screw. I snugged it
up until I could no longer rotate the resistor by hand.
Although I removed the mudguard and the lower plastic fan cover, only the mudguard was necessary for this repair. The finished product looks clean and professional. I suspect that the only reason the resistor comes mounted on the condensor shroud from the factory is that it made it easier to install the fan/condensor as one complete unit with a minimum of external
connections. The new resistor is well away from the newly extended battery overflow and if the resistor ever dies again, replacing it will take 10 minutes, tops.
Thanks again for all your help Randall. You saved me a bundle and I had fun doing the repair. Just wish I had access to a hammer to clear the old fault codes.
Best,
Mike
Battery Drain with Hose Added.jpg
New Resistor Mounted in New Location.jpg
