I have a GFA/AC system. The thermostat is a Honeywell Chronotherm III. It was installed with my system over 10 years ago. It has an AUTO setting that is supposed to switch between Heat and AC. It worked fine for a long time but a few years ago it just quit switching. Other than that it works fine. All the programmable stuff works just fine. The only thing that is not working is the automatic switching from Heat to AC and back. It's up in the 80's during the day and down in the 40's and 50's at night here so it's something that I would like to have working.