I have 528i with the standard heat/ac system. It has 2 vents in the back. When I turn on the heat, I've noticed that it blows hot hair from the front 4 vents, however, it only blows cold air from the back vents. There have been times it blows luke warm air (never hot like the front vents) however for the past month, it just blows cold air from the back vents, even when air is turned as high as it can be. What am i doing wrong? Anyone experience this? My next step is to take it in to be looked it. Note.... the manual says I need to turn some button in the back from blue to red, however, my car does not have such a button below the vents as the manual shows.