I just replaced the heater core in my 1994 Audi 90, the heater was working perfect until I was at a stop light and it started blowing out cold air. I can't figure out why it would do this just after I had the heater core replaced....any ideas? And another problem(actually maybe its not) this is my first audi and I don't know whether or it my blower switch is working correctly, but there are four speeds on my switch and the first two it sounds like nothing is happening with the blower motor but air is still coming throught the vents. The first and second setting don't make a different as to how much air is coming out but it seems to come out the faster the car is going. Then when the car is stopped nothing comes out. The two highest setting are basically high and then super high. I don't know if something is wrong with the switch or if this is suppose to work this way...any suggestions to my problems? thanks!