My AC blows cold air when I'm driving, but as soon as I slow down or stop for any reason the a/c seems like it shuts off and the air gets warmer. But as soon as I take off and am driving again, the cold air comes right back on. What could be causing this sudden change? I do know that the air won't be as cold when just sitting still as it is when driving, but this is a very noticible rapid change.