I have a 2 story home and a lot of heat goes up the stairs. My ac returns are up stairs. If I turned on ac fan only, I get air blowing out of the registers. I tried this once but only felt cool air. In theory you would think the returns would suck in the warm air coming up the stairs and redistribute it through the registers. Question is am I losing to much heat in the cold attic before it moves through the rest of the duct work? Or should I have let it run longer. My wife was home during this experiment and wasnt happy about cold air coming out.