Chevrolet Repair: Heating Problem on 2000 Blazer, blazer s10, velocity changes

Question
No matter what I set the controls on on my 2000 Blazer I get nothing but cold air from the vents. I installed a new Tstat and have a full resovoir of coolant. The line going to the heater core is hot as is the return line. As I attempt to adjust the temp to hot, the air velocity changes somewhat but it remains cold, Any tips or suggestions? 2000 Blazer S10 with a 4.3 engine

Answer
Hi Doug,
Since you have already checked the hoses, it would appear that coolant is flowing, and not air locked.
If you can see down into the radiator on the end where the return heater hose attaches, and verify flow, that would be nice.
Another way is to pull off the heater hose that goes to the radiator, and actually see if it is flowing.
There is a lot of contraversy right now about Dexcool antifreeze, and potential plugging of heater cores, but I really don't think that is your problem.
The way temp is controlled is not with coolant flow...it flows through the heater core all the time.
The air temp is controlled by directing the air flow through or arround the heater core.
I expect that the door that switches that air is not working properly.
I am unsure if yours is digital(electric motor) controlled doors, or vacuum.
But I believe electric.
Either the door is stuck, or the motor is broken.
Some motors move more than one door, with links and springs, and although this isn't much help to you, I believe that is where you will find your problem.
If you verify that coolant is indeed flowing through the heater system, then I am sure of it.
Sorry I can't just say a simple fix.
Van