One thought, have you got automatic air con or manual, if automatic? I'd think that that sensor is to monitor sunlight and so reduce heating when sun is shining. My daughter's Ibiza has manual air con and does not seem to have that sensor, my Passat certainly had one, think the Polo has as well and both of them have automatic air con, I have not noticed a sensor on the S4 though.
Ahhh I have auto, with it being the sport it comes with climate control with the auto function.
Thanks for clearing that up!
Doesn't really work mind as the heaters constantly blow out hot air anyway haha. No idea how to fix this.