AC Compressor casting cracked..what caused?

[mcbit500]

McBit500 post shows it should not be clutched.

My illustration is taken directly from the Denso Catalogue, which interestingly does not list an application for the V6 Cayennes.

If the unit does not have a magnetic clutch it will have a torque limiting slip or fail device, normally termed a clutch. This is designed, dependent on type, to slip or fail in the event of system overload or compressor failure and should reduce the likelihood of serpentine belt failure, yours may already have done so!

I would find it a little odd if both magnetic clutched and direct drive compressors were fitted to identical AC units on the same vehicles as the direct drive compressor requires an infinitely variable supply voltage to provide proportional control of the swash plate and the 'Mag' clutch version requires only a switched 0v/ 12v supply. Just my thoughts, I have no evidence to the contrary

[hahnmgh63]

The post above does say "SE / SL" and then it say's the SE type has no magnetic clutch, which may mean that the SL version does. With enough people looking, I'm sure we'll get to the bottom of this soon.

Edited June 28, 2013 by hahnmgh63

[mcbit500]

According to the DENSO catalogue, (I found the latest one) all 955 Cayennes are DENSO SE type compressors 7SEU17C in the V8s and 7SEU16C on the Cayenne V6s.

A good explanation of the various compressor types and the clutch operation on direct drive units can be found here

Edited June 28, 2013 by mcbit500

[Nylon]

Thanks for the great info....The link to the denso site shows on page 20 that at the very least there is serpentine belt protection if the compressor locks. A limiter breaks allowing the pully to spin free. That is in the diagram on a 7se unit. The diagram indicates that that model is not a clutched unit.

In my search for a new compressor the next problem is what to put back in it? Both the Porsche dealer and the bigger Indy Porsche repair place both told me that the replacement is clutched. All of my searching on the net..mostly e bay...shows the 7seu17c to be a clutched unit.

Now that leads me to question the control aspect. Also makes me queston the information on this unit for e bay which indicates this model works on all v8 and v6 cayennes '03 to '08 which I kinda doubt now. Voltages to operate the compressors must be different between a clutched and not clutched unit. Maybe Porsche senses which unit it controls. I am also guessing that the car needs to be programmed that the compressor / ac system has been replaced.

As long as I can drive it down, I will have Imola. the indy Porsche repair in Minneapolis just put in what it needs....clean everything out and replace compressor, dryer and expansion...o rings. Reprogram. I will know what they put in for replacement and report back.

[mcbit500]

The unit is clutched but not magnetic clutched. If there is a single electrical connection on the body (see below) which ultimately leads to the rear of the unit, this provides the control signal for the solenoid operated proportional valve which angles the swash plate. Please note in the illustrations in my previous post there are entries for clutch type but no entries under voltage which indicates that the clutch is not electrically operated.

If you have a wire going to the front of the compressor connecting to a unit like the second illustration, you have a magnetic clutch.

[Nylon]

Got a couple of pics of AC compressor while looking for coolant leak. Think McBit nailed it on this one. Have the mid body connector that trails off to the rear. The weird thing is that I am able to spin by hand what would be a magnetic clutch in front of the pully. It looks like something catastrophic happened to the "clutch"...crack in the casting with oil and freon leaking out indicates that as well....darn thing sure spins nice though by hand.

[Nylon]

Finally got my AC compressor fixed. I dropped it off at Imola in Minneapolis the evening before so they would have it for the day. I had to drive it home 200 miles the next day. Imola was a very good experience. They are open till 9 PM which is amazing. Everyone was exceptionally nice and very easy to communicate accurately which is a rare thing these days. Via e mail, phone and in person. They replaced the compressor, expansion valve and drier up front. There are three different ports that need to be flushed to do a decent job. There was a ton of crud that came out of my system. They flushed and flushed. The mechanic...Erick...came out when finished and we had a nice long talk. This Cayenne has rear AC meaning that there are more components buried deep which I hadn't thought about. We decided that replacing what we did and flushing the heck out of it was our best angle of attack. There may still be some crud caught in the rear components but should be minimal if any after his mega flush. Very much appreciated his effort. I bought this car and was told that it had a new ac compressor. Well it probably did after the old one h bombed into the system. They just slapped on a new compressor...no other components and no flush nor proper oil at each component. Imola warrants this one for 12 month and seeing as the compressor runs constant with a swash plate rather than a clutch....if its gonna blow due to remnant debris...it should do it fairly soon. I would recommend to anyone doing AC work to bring it in to someone who has the equipment. They finished my rig at 8 PM. It was not cheap but it wasn't that far out of line compared to simple compressor replace and recharge @ $1000 + each for a Honda Accord v6 and a Suburban 2500. We never did an autopsy on old compressor. No time.

[bigbuzuki]

Was the dessicator (receiver drier) replaced as well since air got into your system?

This item removes the moisture that was in your system, but once it becomes saturated, it needs to be changed otherwise there is no more moisture removing protection which can cause issues down the track.

[seafeye]

Maybe i will get in trouble for posting this….but i found it online and is good reading.

This should explain how the Cayenne Air Compressor works along with other things…..

Edited November 29, 2013 by Loren
Removed copyrighted document

[Nylon]

# 1

Yes the drier / desiccator element was replaced. Lines, evaporator and condenser were flushed repeatedly from three separate locations with a pulsing high pressure flush device. Vacuum was pulled for 45 min to remove solvent..then system held vacuum for 30 min. I will mention that it was 2669.76 for the total with tax. Spendy? yes...but less than half of what dealer would have charged and dealer would not have spent the time flushing. Then to have a long discussion with mechanic about ac current and future prospects and full disclosure of his repair are worth every penny.

We also discussed having him replace the plastic T's with a custom brass replacement. They are game to replace the Ts if I fabricate them to darrinsmith's specs which he posted here on renntech. Mechanic also believes that I have leakage past the spring clamps on engine coolant lines...another good conversation.

#2

Great post by seafeye. That is an impressive technical bulletin. Spells out pretty much everything. Added overfilling 134a as another possible suspect in my catastrophic compressor failure. That document should get posted on its own special place for all Porsche owners to read. Thank you!

John

[mcbit500]

Maybe i will get in trouble for posting this….but i found it online and is good reading.

This should explain how the Cayenne Air Compressor works along with other things…..

There are a large number of After Sales Training Manuals available to contributing members here on Renntech.

[seafeye]

Oops i didn't get it from here. Loren please remove if not appropriate.