The AC compressor on my SDL runs all the time, at least at idle, in all modes except economy. It even runs when calling for max heat. I noticed this when I converted it back to R12 and thought something was wrong, but I guess it's okay. It's been working w/o a problem for 3 years. I'm in FL so temps never go much below 45. My original thread with a simliar question.
300SDL ACC question