A failure of the blower motor to operate is a common problem on the 2004 Chevy Trailblazer. The problem, most often, is found in the blower motor resistor or its wire connector. The resistor controls the fan speeds by varying the voltage to the blower. Because of the amount of amperage passing through this device it tends to heat up in operation. The resistor either burns out or the electrical connector gets hot and distorts or melts and makes a poor connection.
Remove the passenger side knee bolster under the glove box. This is the plastic cover and has two 7 mm screws that you must remove with the nut driver.
Look up under the dash and directly behind the glove box, and you will be able to see the blower motor. The blower motor resistor is situated next to the blower motor. It has two electrical connectors, one from the panel control and the other to the blower motor. Use the small screwdriver to push the tab in the connector coming down from the control panel -- the connector opposite the one to the blower motor -- and pull it out of the resistor. Push the tab on the connector in the blower motor and pull it out.
Remove the 5.5 mm screws securing the resistor to the HVAC housing and lower the resistor out of the housing. Check the electrical connectors for distortion or melting and replace them if necessary.
Install the new blower motor resistor and the 5.5 mm screws. Plug the wire connector from the control panel into the resistor. Plug the remaining wire connector into the blower motor. Install the knee bolster with the two 7 mm screws.
