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
Before I got into the heater core I'd check the thermostat first then make sure the heater control is working
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.