Chevrolet Repair: Heater problems, air flow control, heater cores

Question
94 chevy Z-71 p/u - 1500 5.7 liter
Question- heater stopped working, have replaced thermastat and still not working.  Is there a sending unit or sensor that I should check?

Thank you,

Answer
Hi George,
You may need to check the coolant flow through the heater core.
Often you can look down in the neck of the radiator, and see it flowing from the heater hose fitting.
I have heard a lot of talk lately about Dexcool antifreeze plugging heater cores, but haven't personally seen it.
Other than coolant flow, the heater housing air flow control doors are the other possibility. They may just not be directing the air flow through the heater core.
I am assuming the blower fan is working.
Van