2004 Ford Explorer

Heater problem
2004 Ford Explorer 6 cyl Four Wheel Drive Automatic 78,000 miles

having a heater issue obviously. I have a 04 explorer and when I turn my heater on I get air flow but its cold air and there is a tapping sound behind the air conditioning/heater control panel when I turn the thermastate to red (heat). The sound goes away when its turned to blue (cold). Any ideas what that can be?
October 16, 2009.

You have a stuck or damaged blend door. It is what sends the air either past the heater core or the AC. If it isn't opening properly, you won't get heat or AC based on what position it is stuck in.