I asked the same question last week: //heartlandowners.org/showthread.php/33864-A-C-and-Furnace-at-same-time?highlight=Furnace
This is great. since it was 105 when i picked up my Cyclone, I never tried my furnace until this AM (40's). The same thing happened, the AC fan started blowing as soon as I turned on the furnace. I ran into the house and logged on the HLOF, and voila. I didn't know I could change the fan speed, let alone set it to auto for the AC. Also setting it to auto would resolve my furnace issue. What a great resource, especially since we only get a crash course during our PDI's.
BTW, how effective is the AC fan at re-distributing the heat from the furnace.