Why does the heater work, then blow cold air until we reset the temperature?

What is your question?

The heater will work OK for a minute or so, then blows cold air. We can get warm air again if we turn the temperature knob to the highest setting then immediately back down to setting it was at. This will resolve the problem for a minute or two then the cycle repeats.

What makes this problem better or worse?

when cold air blows, turn knob to highest then back to the setting it was at

How long has your 2006 Chrysler 300 had this problem?

years