Auto Air Conditioning & Heater Repair: heating/a/c, chevy blazer, 2000 chevy blazer

Question
I have a 2000 Chevy blazer. When I turn the knob from cool to heat,  the car still blows cool air. And the mornings are getting cool so it would be nice to get some heat to blow in the car.  I have changed the thermostat. Can you give some ideas.

thanks  

Answer
What was the LAST repair on the vehicle ?. ANY repair of any nature ?. In most cases problems that arise days, weeks or even months later can usually be traced back to the previous repair.

What is the past and current reapir history ?. I mean everything, Right down to cleaning the windshield from bugs.

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