Van blowing cold air
It has air in the line. let ir idle with the radiator cap off for a little while and the air will work its way out. You may have bigger issues, but I do not think you need to clean heater core because you get heat sometimes. Do you see a lot of bubbles when you take the radiator cap off when running, head gasket if so.. You can take the cap loose while the engine is running, but not after you stop it, it will be to hot. Good luck
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