heat trouble shooting from @ A/O

[ak_petey]

Ok here goes, at really cold temps I can get semi warm air blowing through my air vents. The engine's operating temperature is pretty normal (running at 180-190'F). On the A/C setting I get plenty of warm air, but cannot run it for too long because it fogs up the inside of the truck.

I was just wondering if I could establish a basic (low cost) trouble shooting/solution thread for getting warm air back in my truck. I was also hoping to get other methods and/or ideas of how to do this cheap.

This is what I have in mind so far:
check thermostat
flush heater core
flush radiator