Aperture's comment and w00t's experience prompted me to check the manual. According to pg. 69, sounds like the compressor may indeed be switching off.

Information on air-conditioning
compressor
The air-conditioning compressor:
– Can switch off briefly to ensure sufficient
engine cooling if the engine is operating under
extreme load.

It does not indicate whether in Auto mode or not, but I've certainly experienced it both in Auto and Manual modes. While I expect this to be the standard operating procedure for any brand of car, I do find it a little odd that it's happened a few times already in the Cayenne, esp since it hasn't been very hot yet here in Vegas. I haven't an experience like this in any other car I've owned. Mystery solved?

 

I have an update on the weak A/C issue. I took my wife's 2011 Cayenne S to the dealer about ten days ago and complained of the following problem:

"We are not liking the performance of the AC on my wife's 2011 Cayenne S. When the vehicle first starts up, the AC blows cold air but very quickly (and prematurely) dials back unless we lower the temperature setting to 65 or lower."

The dealer checked the refrigerant level and found that it was 50 grams low (out of 850 or so fully charged), so he filled it to spec level. Unfortunately, the same symptoms remained. I finally got a chance to take the vehicle back this afternoon, and my service advisor decided to call a Porsche technical support engineer. He told my service advisor that Porsche is aware there is an issue, with multiple complaints coming in especially from the southern part of the U.S. It turns out that Porsche is using an infrared cabin temperature sensor that is located at the lower right corner of the trim surrounding the instrument cluster. It is a quarter-imch or less in diameter and looks like the red plastic on the transmitting end of a remote control.

The problem arises when the air blowing out of the A/C vent just to the right of the instrument cluster is set for unrestricted flow and is pointed directly at the driver. The sensor registers the effects of the cold air on what the sensor is "seeing", which is the back side of the steering wheel and the driver's shirt or blouse. If the shirt or blouse is made of a loose fitting material and/or light colored, the sensor "sees" the temperature of that material (which cools more quickly than the rest of the interior) and prematurely dials the output air back since the sensor thinks the desired setpoint has been reached.

The likely permanent fix is going to be to relocate the infrared sensor somewhere else in the cabin so that it registers something more representative of the overall cabin temperature. The short term workaround is to dial back the output volume of the A/C vent that is just to the right of the instrument cluster and to aim it just to the passenger side of center of the vehicle.

I know this seems somewhat strange, but we tried it on our way home from the dealership with an outside temperature of 98 degrees F, and we were very comfortable with a temperature setting of 72 degrees F.
__________________

 

Thanks a ton for posting this! I'll give the short term fix a try tomorrow.

 

This is great information and makes complete sense. I'll make sure that mine is adjusted properly too until there is a better fix. Thanks for your effort.

 

Great info, solved my issue as well. This may explain why some have the "problem" and some don't. Thanks again.

 

Here's an update on this. Porsche now has a fix available for the issue I described in Post 17 above. I went to a different Porsche dealer, who told me the real issue is that the back of the infrared sensor (behind the dash panel) is getting chilled by the air from the AC vent just to the left of the PCM and is prematurely cycling the AC because it thinks the setpoint is being reached even though it actually hasn't. The fix is for the dealer to apply a Porsche-supplied felt circle (with adhesive backing) to the back of the temperature sensor to in effect insulate it sufficiently that it doesn't react incorrectly.

I'm not sure how this jibes with the previous explanation that was given to me, but I had the fix done this afternoon, and so far, the AC system seems to be functioning properly, even with the air volume on the vent set to full open and with the vent blowing right at me. I waited at the dealership while they applied the fix, and I was in and out in an hour.

By the way, the dealer says they just heard about this fix a couple of weeks ago.

 

Never had a problem w A/C in my pepper
Love those ventilated seats too

 

It's 104 in Houston this afternoon, but I just drove home in 72 degree comfort, complete with the vent to the left of the PCM blowing right on me. Yes!!

 

Thanks for the update.

 

Could you please post a copy of your service invoice or the number of the TSB performed?

 

Yes, I'll try to get a PDF and post tomorrow.

 

+1, thx.

 

As requested:

 

By the way, the above PDF indicates that the actual fix is to trim and place a rectangular piece of adhesive-backed felt to the outer side of the AC vent to prevent cold air from reaching the back of the temperature sensor.

 

So for those of us that have not yet picked up our 2012 orders, will they do this now at the factory during build, upon delivery at port, or automatically at the dealer? Or do we need to experience it and then go ask for it?