so I have a 98 blazer. Last year when I got it from my dad the heater wasn't working. We replaced to heater core and flushed out the radiator a couple of times and replaced it with good anti freeze until the heater ran good.

Well this year I went to turn on the heater and what do ya know, it is doing the same thing again.

So is there anything else that might be wrong with it or do I just need to flush out the anti freeze and start over

 

You could have a blend door not working, or working when it shouldn't. Are the heater hoses hot both of them?