The blower fan (inside unit fan) on my Lennox AC unit won't run. I discovered this when the AC wasn't cooling and I found the refrigerant line was frozen. After waiting a few days for everything to melt, I saw that the outside condenser unit is getting power (and still running, thank goodness) and the furnace below the evaporator is getting power. Is this a simple "replace the fan assembly"? Or should I pay $100 for a professional to take a look at it. The refrigerant level was checked only 1 month ago, and found to be OK.