AC/Heater problem

[stanbu815]

Have a 96 w/93K miles. Bought it in 2002 and never had any heating or AC problems. I live in Chicago. Sometime early Spring 2008, I noticed that the Temp Control was not adjusting the temperature but I was getting enough heat to at least keep the car comfortable. It was getting warmer outside so I avoided doing anything. In May, I tried the AC for the first time since last year's cooling season and it worked fine except I couldn't control the temperature even adjusting the control from max to min temperature. However, ever since May, the compressor often doesn't kick on until after a few minutes but once it is on, it stays on and I freeze. When it won't initially kick on by pushing AUTO, I try DEF and it won't kick on with that setting either. It does not appear to be a compressor or refrigerant problem but rather a control problem. There is no check light on.
I read about Sensor failures. Could that be an issue? Remember, the Temp Control stopped working first and unless the Sensor controls the Temp Control, I didn't see that as a problem but who knows? I also read about a Control unit that gets stuck. Could that be the problem?
Anyway, before I go to my favorite mechanic who is not an SVX expert but has done good work for me, I thought I could give him an idea of what to look for.
Can anyone help me?
Thank you,