Windshield would fog up and the defrost vents wouldn’t thaw it out. Noticed a coolant leak coming out of the heater core so went ahead and pulled the dash and replaced the heater core. Got it all put back together, had heat for about 10 minutes, lost it and the windows still won’t defrost. Tried burping the system best I could. Was wondering if it was maybe a thermostat issue? Or is there something I’m completely overlooking? Any help is appreciated

 

Is there warm air coming out if the dash vents?

 

it’s just barely warmer than the temp outside

 

Air pocket in the heater core, or blend door malfunction.

What year is your truck?