im have problems with my a/c system on my 323i 1999.first when the engine starts and turn the a/c on it blows cold air driver,center,passenger vents,but when engine warms up or in the middle of noon hot air blows in the center vents and when i turn on the switch to manual by pressing the 2nd and 3rd button on the climate control hot air comes out on the floor and cold air in both left,right,center vents.can anyone give me some tips to diagnose this problem