I've driven two 960's with this issue. In some cases you can avoid by not running the system on auto. You have three dials, one for fan speed, one for airflow direction and the other for temp. Try setting the fan speed or airflow direction off auto; it does not matter what the temp is set at. Also, avoid the recirc (turn it off) when accelerating (note that when your pass compartment is hot and you have the system on auto, the recirc is on). I find that if I leave the airflow at face and the fan on auto, everything works (to include once the car temp has cooled to the approx temp setting, i can put it back on full auto and it works as long as the temp does not drop enough to force the recirc on). Note that I have used this method for two years in sunny El Paso, TX where the summer temps are always close to 100 degrees (+ or - 5 degrees). Hopefully, your problem is caused by what causes mine.

Good luck.