Is the a valve on 2001 blazer to release air from heating system?

I have a blazer with no heat, I have replaced the thermostat, temperature control and flushed the system yet no heat. Prior to replacing the temperature control I had a little heat if I moved the control around, I doubt it is the heating core, I was told to let the air out of the system by a valve; however, I... show more I have a blazer with no heat, I have replaced the thermostat, temperature control and flushed the system yet no heat. Prior to replacing the temperature control I had a little heat if I moved the control around, I doubt it is the heating core, I was told to let the air out of the system by a valve; however, I don't know where the valve is?
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