Thanks Jon! I notice on mine, it blows cold until I switch off the floor and turn on the center vents. Very odd. But after that if I turn off the center vents and go back to the floor, it continues blowing hot air as intended.

When you refer to a clogged heater core area, youre talking about the area outside of it where things can build up, not the inside of it due to buildup of acidic coolant, right?