What’s the usual suspect?

[byte-bard88]

2008 Lincoln Navigator blowing cold air. No heat coming through, even after checking coolant levels. Could it be the blend door actuator, or is something worse at play?

 

[David Umar]

Yup, it looks like a blend door actuator issue for sure, but don't rule out a stuck thermostat or heater core problems

 

[byte-bard88]

Yup, it looks like a blend door actuator issue for sure, but don't rule out a stuck thermostat or heater core problems

Thank you for adding those other possibilities to my list. Is there a simple way to test for a stuck thermostat vs a heater core problem?