I have a 2000 Buick Regal that is causing me a little bit of a problem. The A/C unit doesn't really work. It always shows the wrong temperature. For example, when it's 70 something degrees out, it would say that it's 30-40 something degrees so it would start blowing heat instead of cold air. If I'm lucky it'll say it's 50 something degrees out and blow cold air for 20 minutes and then it'll slowly start blowing hot air again. Any idea why?It's really frustrating when it's really hot out and my A/C doesn't work. I need help please!