I usually keep the temp control on economy. As the engine heats up hot air comes out of the outside dash vents and gets hotter as the car warms up. So far, so good. Here's where it confuses me. After a few minutes of hot air, it starts getting cooler until it gets too cool for comfort. Let the car sit for a couple of hours, start it and cool air again. Let it sit overnight, start it and as the engine warms up, hot air for a while,then it cools off again. I can adjust the dial inside for a hotter/cooler temp, but it just seems to either keep the hot air coming in a little longer or a little shorter period of time. It doesn't "level off" and keep the car at a set temprature. It's either hot air of cool air--nothing in between. Any suggestions ?