Kicked on the A/C early this a.m. Noticed when I got home 5 hours later the house wasn't very cool and little air flow coming from the vents. Went down; checked the furnace. Frozen! My first thought was filter or low freon. Not low on freon and filter new. Once ice melted, kicked motor on again. It ran, then inside furnace area area froze again, blocking most of the air flow after a few hours. Sounds like motor running slowly; very little air flow. A/C heater system installed in 2000. Any ideas? Thanks for the help.