[Billski]

2008 GP with standard basic HVAC system (not auto temp, not dual) suddenly started blowing only lukewarm air when heat set to full. Engine temp in normal range, thermostat operating normally, heater hoses both feel hot. Radiator checked cold, completely full, no signs of Dexcool sludge at filler neck. Cooling system has not been opened for any service/repairs.

Checked the blend door actuator, it responds to every setting. When temp control turned to full hot setting, can hear the blend door closing against the seal and the positioning notch on the actuator shaft points straight down (I believe that's the index mark for full hot).

Everything else about the HVAC system works fine. Fan runs at all setttings, heat/dash/defrost vents all function normally, interior air recirculator functioning normally.

Other than back flushing heater core, followed with flushing/changing/bleeding coolant system, any ideas?