Brett968

The first fault (4WD System Faulty) triggers the fault in the PSM system. In other words, the problem resides in the former. The 4WD system electronics in these cars is essentially just the transfer case computer and the transfer case servo motor (+ rear lock diff if so equipped). Problems with these components are very common, especially in early year Cayennes. There are a number of threads on this topic, such as this one from a few days back: Your fix is most likely replacing the transfer case servo motor and transfer case ECU. Any competent shop familiar with Porsches and owning the correct tools should have no problem diagnosing and repairing this issue. Both of these components can be replaced in under an hour without even needing the car on a lift. Brett

Most likely your transfer case servo motor has bit the dust. It's pretty easy to remove and open up to inspect. When mine went one of the motor windings had melted. If/when you replace it, make sure to replace the transfer case ECU at the same time. Supposedly there is a design fault in the early transfer case ECUs that can cause them to burn up the servo motors (hence the TSB mentioned above). You may be able to find an updated transfer case ECU on eBay, otherwise you will need to order it from the dealer. The good news is that both the servo motor and the ECU are very easy to replace. Brett

The trailer wiring harness is prone to fraying against the metal bumper support on the passenger's side near where the wiring enters the passenger compartment. Clarksongli suggested a few other places to check. It might be worth taking the rear bumper cover off and having a look. Your alarm issue could be related. If a trailer is sensed when the vehicle is locked then the alarm will be armed and go off if the trailer is removed. If the wiring is frayed and making intermittent contact then it could cause the behavior you described. Brett

The pictures of the CCV you posted look very similar to the part that I found that fixed my problem. I believe there are only a couple of variants of the CCV for the 7SEU17C compressor that have pigtails, so it is likely that you ordered the correct part. As I mentioned in another thread, I can confirm that the Gogoal ECV03C is correct for our cars and it is readily available in North America. My car had very weak cooling. I replaced the expansion valve but this didn't fix the problem. With a new CCV the cooling has never been better. Even with temps in the mid-90s and a car full of people it has no problem maintaining 71 deg and in fact does so with only mid fan levels. Oh yeah, my car has 245k miles on it, original compressor. Brett

In the case of my faulty CCV, high side pressure was slightly low but low side was clearly too high (it should be 20-35 psi or so). This is consistent with what you are seeing. Your low side pressure is even higher than what I was seeing but this could be explained by your higher ambient temperature or it could be that your CCV is simply in worse shape. Does your rear A/C work? There are two expansion valves with the 4-zone climate control, one for front and one for the rear. I would expect that both expansion valves would have to be blocked to cause what you are seeing. Considering the damage that the lines sustained, I guess this isn't out of the question. The front expansion valve is underneath the passenger's side wiper. It's fairly easy to replace. I tried replacing the expansion valve first when I was diagnosing the problem with my car. It wasn't the problem. I think a faulty CCV is a reasonable guess in your case but it could really be anything considering the fact that the valves were so badly mangled and debris could be anywhere within the system. Good luck! Brett

One pump went at 170k miles. Replaced both at the same time.

Have you checked for faults in the gateway control module? Brett

I'm afraid Loren is right. Do you know anyone that has vagcom? That should also work in this situation due to chassis sharing with the Touareg.

Make sure that your OBD2 tool is specifically querying the HVAC computer for fault codes and not just the engine computer, etc.

I don't recall. It's been a few years. Sorry...

You might also want to pull the transfer case motor out and take a look at it. Takes like 10 minutes. As I recall, it is really easy to open the motor and inspect it once you have removed it from the car. On my Cayenne a winding on the stator had melted, rendering it inoperative.

OK, I am going to assume then that the compressor is being driven (pulley isn't freewheeling around the compressor shaft like the OPs). A Durametric tool would be really useful at this point. We would like to know whether the climate computer is requesting refrigerant flow or if it indicates some fault elsewhere (e.g. bad pressure switch, etc.). Do you have access to a Durametric tool? Even just a basic fault code reading of the HVAC computer with any compatible OBDII tool would be better than nothing. If the climate computer doesn't point to any other apparent problems then you may want to look at the compressor control valve. This is the part that fixed my car. I suspect a number of other Cayennes are plagued with weak or inoperative A/C due to this valve malfunctioning. You can source the valve from a few places online. Note that there are several different versions of the valve for Nippon 7SEU17 compressors (the type in the Cayenne) depending on application. You need the one with the pigtail connector. I know that the Gogoal ECV03C is one option that works for these cars and you can get it for $42. To replace the valve, you need to remove the refrigerant, replace the valve on the compressor, change the drier and then recharge the system. The valve is held into the compressor with an internal snap ring and is very easy to replace. Do not attempt to remove the snap ring while the system is pressurized or the valve could become a high-speed projectile! The valve can be replaced with the compressor in the car but I found it was easiest to remove the compressor (only takes 15 minutes). A good shop should be able to do the whole job in a few hours tops. (BTW, the pigtail on the replacement valve was 0.5cm shorter than the original. I had to flip a wire retaining bracket around 180 degrees to make it reach.) Having said that, it is quite possible that something else is wrong. I would try to get all the diagnostic information I could before throwing any parts at the problem. Brett

ricurt, The compressor doesn't have a clutch. The wires that you found are for the compressor control valve. Read my reply in this thread: Brett

I recently successfully self-diagnosed and repaired the A/C on my Cayenne. Total cost for parts and refrigerant ~$65. Vent temps went from 17 C before the fix to 4 C in ~24 C / 75 F ambient temps and high humidity. I will post details on the fix and the way to diagnose this particular problem (and other HVAC issues) in a new thread. Anyways, one thing I discovered is that there is a lot of incorrect information out there regarding the HVAC system on these cars. One of the more pertinent items: The Cayenne uses a variable displacement compressor with an electronic compressor control valve for modulating the mass flow of refrigerant through the compressor. There is no compressor clutch, so to speak. This is not like the old compressors that we are all familiar with that use an electric clutch to cycle the compressor ON/OFF. Please gently slap anyone who talks about an electric clutch on the Cayenne compressor. If you are in doubt, just do a google search for "Cayenne AC compressor" and look at the pictures. There is only a single electrical connector and it routes to the back of the compressor; this is the compressor control valve. The HVAC control unit adjusts the refrigerant flow to meet the required demands. Instead of cycling a clutch on and off, a swashplate inside the compressor adjust the stroke of the compressor pistons to realize the specified refrigerant mass flow. No more ON/OFF cycling, just nice consistent cooling--in theory, at least (and when everything works). Fuse 11 that Loren mentions powers the compressor control valve. The negative lead goes to the HVAC control unit. The valve is driven by a PWM signal, likely current controlled. To the OP (Bichito): Sorry to say it, but your compressor is toast. The part that you are referring to as a clutch is actually a sacrificial break-away mechanism. The idea is that if the compressor locks up then this part will break in two and allow the pulley to spin so that your other accessories are still driven. I can think of no other scenario for your situation other than a catastrophic failure of the compressor. If you are lucky, then the compressor didn't spit it's guts throughout your refrigerant system. Either way, you will need a new compressor (and drier, at a minimum) and a very thorough cleaning of the refrigerant system (get this part wrong and you may be doing the whole job over again). Sorry... @neoplanet: Your problem may be far less serious but we need more information. You wrote that the A/C shop said that everything checked out OK. What does this mean? I'm assuming that this at least means they did a visual inspection of the A/C compressor and did not see anything obviously wrong (like what Bichito found). Did they give you any pressure numbers? Do you get any cooling whatsoever? You wrote that they said there was no voltage going to the compressor. I'm not convinced they checked this correctly. First of all, hopefully they realized that the connector they were looking at was for the compressor control valve (not a clutch, as it doesn't have one). According to the manual that I have, +12 V should be on the red/white wire. Now, if they disconnected the connector and attempted to check the voltage across both leads then they would likely run into a problem because 1) the valve is controlled by a PWM signal (you need an oscilloscope, not a multimeter) and 2) the control valve is most likely current controlled: if you take the valve (which is low impedance) out of the circuit then the computer will recognize this as a problem and probably will not drive the line low. I would totally expect them to find 0 V if they tested things this way. You can test the +12V wire by connecting one lead of a voltmeter to the red/white wire and the other lead to anywhere on the car that is grounded. To properly test that the electronic signal to the valve, you need to keep the valve in circuit and probe across both wires with an oscilloscope. Frankly, I wouldn't waste my time doing this at the moment. First thing I would do is get some pressure readings. If your high side pressure is OK then you can forget about the electrical checks on the control valve. Once I know your pressure readings I can make a suggestion as to what I would check next. Brett p.s. To address the original question, there is no A/C relay on the Cayenne and therefore no "A/C relay location". :) Edit for clarification: I should have said that there is no "A/C compressor clutch relay". I also just noticed that this thread was a year old. Oops!

With the refrigerant evacuated and the system open, there shouldn't be any pressure holding the plug upward. You will still have to make sure the plug is slightly depressed to remove the circlip. There are ridges on the cap that prevent the circlip from being removed when it is in the normal upward position. This is to prevent the clip from being removed when the system is under pressure. To press down on the plug, I think I just used a long 3/8" extension (no socket) with the open end facing the cap. In my case, the refrigerant was evacuated but the system was not open. I had to hold very light pressure while removing the circlip. In your case, I'm wondering if you can't just push it down and it will stay. Perhaps the slide hammer is for removing the plug? I could see the plug getting stuck in the downward position if the system is open.

Your 1592 fault code suggests to me that the motor controlling the fresh air recirculation valve is also faulty. If fresh air is entering during cooling instead of recirculated air, perhaps this is why it isn't blowing as cold sometimes? On left-hand drive cars this motor is mounted on the blower motor assembly and is very easy to replace (5-10 min). It is the same style motor as all the flap motors mounted on the air distribution box.

The entire job is done from below- no need to remove the dash panel. I would recommend acquiring the workshop manual before attempting. Another advantage of purchasing the entire heater core assembly is that you can easily see how everything goes together on the donor assembly.

It's the flap motors. There is an air distribution box under the dash in the center of the car; the valves are mounted on either side of this assembly. The valves were redesigned for MY2005+. From the research I did while dealing with this problem on my own car, I concluded that the earlier revision valves fail at an exorbitant rate while the revised valve appears to be very reliable. You could chase the individual fault codes and just replace the motors that are reporting problems. This will be a waste of time and money- you will eventually end up replacing all of the motors. It also will be expensive at ~$150 each (last time I checked). Here's how you can fix the problem for a reasonable price: Purchase a used heater core assembly off ebay from a MY2005+. I got one out of a 2006 for $145 shipped to my door. There is a 2-zone and a 4-zone variant so make sure you get the right one. I stripped off all the motors and then just tossed the plastic housing bits in the trash. I had six separate error codes before the fix. The climate control system has been error code free for the past 1.5 years and I saved over $1k. Most importantly, the climate control system has worked perfectly during this time. You can replace the motors yourself (I did) if you're mechanically inclined but the job is a bit tricky and will take half a day or so. Brett