Holidays and Traditions What is AFO and AFI? What is AFO and AFI? The switch ships with two fan modules and a DC power supply, each with a label AIR OUT (AFO). ... The switch ships with two fan modules and an AC power supply, each with a label AIR IN (AFI). Related Posts:How do I wire a 3 way switch with red and black?Problem: Fan Blower will not come on in the "On", what to do when a furnace blower fan won't start?Should I remove fan leaves during flowering?How long will the internal battery last in a nest thermostat?