from the manual for my thermostat:
"Special Features
Auto Fan
When auto fan is selected the fan speed will vary depending on the
difference between the temperature set-point and the room temperature.
In auto fan the compressor and fan cycle On and Off with the
thermostat.
When the difference is:
>5º The fan operates on HIGH
<4º The fan operates on LOW"
The fan will stop and restart when it changes speed and the compressor will continue to run. Thought it was broken like most when I first got my current rig.