No Heat

2002 Galant A/C 75,000 miles. Noticed today I have no heat! Normally when I change temperature, I hear the temp motor turning.(Second motor, first changed under warranty). I checked the heater hoses and they were NOT hot. My question: does the temperature control motor control water flow, or is it a door mixing heat? Where could I learn more about my HVAC system in my 2002 Galant? THX,