I have no heat at all. used to work until I had a coolent flush a few months back
step by step how to replace heater core on 1999 chevy s10 pickup on 1999 Chevrolet S10
Try flushing the heater core itself first! It is major repair for a seasoned mechanic to replace that core!! Check youtube for a video on flushing it out.
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Before I got into the heater core I'd check the thermostat first then make sure the heater control is working