I have a new Carrier Infinity system. Even though there is only one (evaporator) coil in the plenum (no reheat coil), it can operate in a dehumidify mode. In normal "cooling" mode, the fan runs at its highest speed, just as you would expect, in order to prevent the evaporator from icing up. From what I could find in the technical manual the installer left behind, it seems that in dehumidify mode, the fan intentionally runs at a slower speed. I've often noticed the compressor running with the fan running at a low speed, and if I look at the thermostat, it indeed shows that it is "dehumidifying". I've also noticed sometimes the fan running at high speed without the compressor running.
My question is:
If the fan is supposed to be running at high speed to avoid icing, why would the system be intentionally set up to run the fan slower? Doesn't that risk icing? Is it an acceptable consequence of trying to get as much moisture as possible to condense out onto the coils? What exactly is the system trying to do and what is likely happening when it is in its dehumidify mode?