Bad Moon, in my rig, it is impossible to run the A/C at the same time as the Furnace, since my climate control's mode switch options are Fan Only, Cool (A/C) and Furnace meaning the mode can only be one at a time.
When in Fan Only, the furnace fan circulates air from the furnace without heat or cold. Cool means the overhead A/C unit can operate and operates independently of the furnace, then finally when mode is set to Furnace, means the furnace fan can run and turns on the furnace heat as needed. There are other selector buttons for selecting other parameters such as automatic/low/medium/high fan in Cool mode depending in what mode you have selected.
I suggest you post all the selector buttons on your unit, then we might be able to help you decipher how it works. I, for one am already confused with your setup if you are able to have the A/C AND the furnace running at the same time. that doesn't seen right unless you have a truly automatic system that turns on the Furnace or the A/C depending on your settings. I lived in a house that worked this way and while it was nice and automatic, once furnace or A/C worked but never both.