Truck Repair: Heater, radiator tank, chevy siverado

Question
I have a 1999 Chevy Siverado 1500 4X4. The Air conditionong worked great in the summer. Now that colder months are here i swith it to hot air and the heater only to find Cold air coming out. The coolant lewvel is fine, I changed the thermostat, Truck is not over heating or anything, However it still blows cold air. What can i do!

Answer
If your heater return hose connects to the radiator tank, just below the radiator cap, draw enough coolant from the radiator to uncover that tube, looking down inside the radiator. Then run the engine, while it is at operating temp, to see if coolant is flowing through that hose, which means it is flowing thru the heater core.

If it is....(and you should also be able to tell by just feeling that hose to see if it warms up, but seeing is believing), then the doors that control airflow around or thru the heater core would be the problem.

Van