I have experienced this problem and have done quite a bit of testing to see if anything I do increases the likelyhood of the rear fan switching itself from a low setting to its hightest speed.Document ID# 1951479
2007 Saturn OUTLOOK - 2WD
Subject: Rear HVAC System May Come On Unexpectedly - keywords
A/C a/c blower control heat heater intermittent unwanted
#PIT4335 - (04/03/2007)
* The more the front center armrest is extended toward the rear seats, the greater the occurence of this.
* The detents of the rear fan control were always fully engaged - so they are not a factor.
* It occurs more often when you have just gone over a significant BUMP in the road.
* It also occurs even if the Rear Fan control is at a minimum position and the rear control has not been touched since the car was started. ....so something is causing the system to think there is a need for full fan on.
I can correct the problem by turning the AUX button from ON to OFF...then back on again, but sometimes I must do this 5 or 6 times in an hour.
I hope that this info helps someone in engineering figure this out....but it would appear that there is a glitch somewhere that is causing this to happen rather than an intermittent issue with the rear control panel.