Cayenne defroster inadequate?

[jvmcnair]

We have a 2013 Cayenne S that spent it's first years in California. Now it resides with us in Park City, Utah where the winter climate is much more severe. It has recently come to our attention how poorly the defroster works, like when driving into a snow storm or heavy rain. The windows fog within seconds and even using the windshield defrost button can not be cleared for several minutes. I think the reason for this can be found in the manual on page 70-71. There it tells me that the A/C compressor "switches off at temps below approx. 38degrees F". Previous to that it tells me that air recirculation mode is deactivated below approx 41 degrees F. I am convinced this is absolutely the wrong way to defrost the windows, or to keep them clear! The A/C needs to run even when it is cold outside in order to dehumidify the interior. That's how my Ford F-150 works and I believe is how my 2000 Carrera works. That is A/C on and recirculate to dry the air inside the car. OK, any other ideas? Anyone with similar problems?

[island911]

There is not a lot of moisture supported in the air even at 100% rel humidity (at 38F.)

If you have a leak somewhere (ingress into the heated space) then you could have high in-cabin humidity, and a tough time defrosting w/o a drier component to the HVAC.

[jvmcnair]

Thanks for that reply; I think you are on the right track and it looks like this thread will become about theory, at least until I visit the dealer. I doubt they will find anything wrong so I will need to insist on talking with a factory rep. Porsche's hot-line has told me there is no other route and it does make sense for them to insist on their dealer's opinion first. Not a lot of moisture? Well, how much does it take to fog the windows? A leak somewhere? As in outside air coming in? I'm sure there is a big leak starting at the intake in front of the windshield. Apparently the HVAC will not stay in 'recirculate' so an unlimited supply of moist air flows in, starting in the form of rain or snow. I think your comment "without a dryer component to the HVAC" is quite accurate. I fear that Porsche has incorporated a seriously flawed design in this HVAC. I hope I'm wrong and this dangerous flaw can be fixed. Jvm