So it's getting hot here, around 95F, and when I start my CTTS and put the fan on high, the fan speed is at its highest. However, even if both controls are on LO, 65, 67, 69...it doesn't matter...the fan spins down to a medium/medium-low speed. The car is still hot inside. I assume it would slow down when the desired temp is reached, but it slows down and it's still hot inside.

Can anyone point me to the problem or in the right direction?

 

Check blower resistor and climate control module first...

 

There's also a setting in the menus to control how hard the fan blows. I'm not with my Cayenne at the moment so can't direct you further.

 

Followed by the blower motor.

Mine did the same as yours, although it was usually accompanied by a groan, intermittently and i replaced my blower motor ($140 and 20 minutes) a couple weeks ago and it works great so far.

 

06 Cayenne S
Replaced blower motor with VW Toureg Part
Resistor with Porsche part from Pelican
This was the best pricing value I found
Fixed my issues in 20 minutes.
Lots of write-ups on DIY, search is your friend