Installing a Honeywell Wifi thermostat and need a C wire connection
In the picture below you can note that the connection labeled with a 7 in a triangle is the "C" of your fan controller. As per your added note to the diagram this is also connected to your A/C unit so there is a common "C" between your A/C and the fan controller. This same place is where you want to connect a spare wire to run for the "C" terminal on your thermostat.