AC Compressor question

I have 97 GT. I noticed that my AC compressor is always running when my dual zone is on. Is this normal? AC works great, but sometimes the coil freezes up and I have to shut the system off till it melts. Blower fans and all vents seem to be working good.On my other vehicle(Ford Ranger)The AC compressor cuts in and out while running.

My 99's compressor does the same thing, but I've never had an issue with the evap core freezing. You may have some mildew or dirt buildup blocking airflow through it that is causing the freezing.