Porsche Yoga

September 18, 2016


In need of a way to keep active I accidentally hit upon Porsche repair. HVAC work on the car demands long periods of kneeling on a matt with repeated stretching activities rather like yoga, so I have coined “Ruby Yoga” as the generic term for hours and days spent on this magnificent and exasperating puzzle which is an early model Cayenne.

16 September, 2016, evening

This morning ticking noises from the dash drove me to remove the glove compartment and associated trim in search of something I could bang into place and correct the problem.

I must specify that I haven’t road tested the car at this point, but in the case of the actuator attached to the white plastic rod, I removed it and discovered it was jammed at one end of its travel, so I pried the case apart with a couple of fine screw drivers.

The first of the many actuators (known on eBay as “AC Boxes”) opened up like a lunch box, revealing contents in good condition.  Because of the triple-reduction worm gears I couldn’t wiggle anything, so I popped the gears out and played with a tiny 12V battery and fine telephone wires, laying the bare contacts along the two poles attached to the end of the motor. This worked, so I added a couple of dabs of white grease to the gears and sent motor power along to the complex part at the other end whose gears also appeared to be intact.


Reversed polarity moved the arm back, so it seemed that the mystery part would still function.  Of course the touches of 12V were very brief, as the travel of the actuator is short, so I simply turned over my pair of wires to reverse the motor to complete each cycle.

After I had played with the thing enough to get the grease worked around the gears, I popped the top half of the case back on and put it back on the car.

When I turned on the key and experimented with heater buttons, the “recirculate” and “fresh-air” buttons caused the device to open and close an unseen flap by alternately pushing and pulling on the rod.

My harassment of the other actuator more properly falls into the burnt-fingers-methodology classification.  I could hear the thing trying to cycle, but I could only see the top of a white arm, or lever, where it joined a black box.  Let’s call it an arm for now.  It appeared to be stuck, with a wire or spring over the top of it.  I could just see one end, so I grabbed the scope and started probing, seeing if I could get a better idea of how it worked.  Wary of short circuits, I attempted to put tension on the spring with the lens of the scope, but opted for a forked green twig about ten inches long.  It moved the spring around in a satisfying manner, and it eventually settled in what looked like an appropriate slot from my perspective.

Further examination with the scope revealed a dark something connected to the white arm.  At first I had thought the arm wasn’t working because it had become disconnected from whatever it was supposed to push, but there was something dark and plastic moving around, enclosed by the white nylon.  So I bumped into the assembly a couple of times with the scope.  Didn’t seem to hurt anything.  I cycled the temperature selector from low to high.  The assembly seemed to be moving both ways now, and began to complete cycles.

I set the temperature  for 16 degrees, half-way on the dial, and called it a day.  I had unwisely taken the lower half of the dash off the driver’s side and would need to re-assemble it before any further testing, so I did that and then called it a day.

After breakfast I’ll take the Cayenne for a test drive and report further.

17 September, 2016

Still no heat in driver’s footwell.  The mystery actuator isn’t cycling this morning, so further examination is in order before I reassemble the right lower dash.‬

It stayed quiet at 16 degrees until I turned the heat up.  Then it started making noise again.  At MAX it quieted down, but provided no heat on the left side.  Chances are a part needs to be removed and examined, if not replaced.  There are sets of seven of these AC Boxes for sale used on eBay for $100.  I’m thinking about buying one.

Must examine the manual again.  Seems the actuators are bolted in groups to a metal plate which can be removed from below, though how and where is beyond me at this stage.

The manual keeps departing from illustrations of the actuators on their plates to show this heat exchanger which doesn’t look anything like the one behind the glove box. It explains how to remove one screw and open the thing to make space for the removal of the plates with the many actuators attached. Turns out the diagram refers to a small black plastic box way back in behind the obvious stuff, and there was no way on earth without a 5 mm box end wrench (I think) to get that screw out.

So I worked around it. There was room. Devilishly difficult job removing the two screws holding the plate for the single (surprise) temperature mixing solenoid, though. Took all day. For some reason my predecessor had installed one of those Porsche safety screws, a torx with a centre post, to guard access to this area. The manual had it as a Phillips. Fortunately, my Porsche-loving son has a set of them.

Once out, it was a simple matter to revive the actuator’s jammed mechanism, though. The white part of the hot air-blending adjustment mechanism plugs into a black box in there. The actuator arm is the mysterious black thing I couldn’t see yesterday. I reached in and wiggled that white arm and it came off in my hand. Seems it’s been repaired before and the O-ring which supposedly holds it in place no longer exists and there’s some wire holding it together. I carefully meshed the geared shaft back into the gears inside, still without the O-ring. It’s a bit reassuring to know that even the pros occasionally become desperate enough to jury-rig stuff on Porsches.

Equipment suggestion: a regular torx screwdriver is too short to reach the first screw holding the plate. For reassembly I used a Phillips screw and a long, thin screwdriver I use for assembling door latches.   I taped the screw to the driver and had it jammed in place within a half-hour. Easy.

The second screw? I left it for later. Figured I’d be back with an O-ring if the thing worked. Interestingly, I found the second screw had been so hard to remove because it had been jammed into the surrounding plastic moulding rather than into the metal clip which had come free of its slot and was sitting below. I could feel for my predecessor in this situation: he was on the clock; I have all of the time in the world.

Equipment suggestion: without the scope I would have had no hope of locating, let alone removing, that second screw. I used a 24” flexible device which takes screwdriver bits and holds them magnetically. It was too long for comfortable use in the Cayenne’s cabin. Perhaps if I had removed the passenger seat things would have been easier.

 18 September, 2016, 9:30 a.m.

Ruby’s back together and no worse for the wear I inflicted upon seats and doors. Cabin courtesy lights work normally, and no warning lights have appeared on the dash. I half expected a screen to pop up: “Unauthorized goon has tampered with HVAC controls!” Maybe that will wait until Ruby is fully warmed up.

For now, the AC blows cold all over and the annoying ticking in the dash has measurably reduced. No doubt I’ll have to go into the left side to get the rest of the clicks and some heat to the driver, but that will be an adventure for another day after I have acquired a few small tools and perhaps a set of used actuators, or AC boxes, as they call them on eBay.

Tool wish list:

5/5.5 mm box end wrench

Torx size 20 (safety) screwdriver with a long shaft

Set of replacement actuators for AC

Annotated Bibliography

2003-2008 Porsche Cayenne Repair Manual sourced online for $15 US, it proved to contain valuable and occasionally accurate information, at least on the mysteries of the HVAC system. The big surprise was that my car Ruby contained fewer of the offending actuators than the diagrams promised, and it made no mention whatever of the first one I worked on, the actuator bolted to the big air box sitting behind the glove compartment. But it told me the location of mystery screws so that I could locate them with my scope and labour to remove them.


One Response to “Porsche Yoga”

  1. Tom Stutzman Says:

    If this post was a pot boiler love novel, it would win a Pulitzer Prize.

    Sent from my iPad


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