This 2006 Chevrolet Trailblazer came in with the complaint that the blower would not work after the blower resistor had been replaced. This Trailblazer clearly has manual HVAC controls.
However the customer was sold the wrong part or asked to buy the wrong part. I do not know which for sure. The part on the floor board in the next picture is a blower speed controller for a vehicle that has automatic HVAC controls. Luckily, I was able to install the correct blower resistor and a new harness connector with no damage to the vehicle system. I would suspect however that the blower speed controller is no longer any good.
The blower speed controller for these vehicles with Auto Controls:
2004-2006 Buick Rainier
2003-2009 Chevrolet Trailblazer
2003-2009 GMC Envoy
2003-2006 Isuzu Ascender
2003-2006 Oldsmobile Bravada
The blower resistor and repair harness kit for these vehicles with Manual Controls:
2004-2006 Buick Rainier
2002-2009 Chevrolet Trailblazer
2002-2009 GMC Envoy
2003-2006 Isuzu Ascender
2002-2006 Oldsmobile Bravada