This 2004 Chevrolet Silverado came in with the complaint that the blower motor will not turn off even with the key off. This is relatively common problem of the the full sized Chevrolet, GMC and Cadillac trucks with auto a/c controls. The first step is to lower the passenger side hush panel under the dash. There are three screws with 7 mm head on them. The one over the transmission hump is slightly difficult to remove and can be a SOB to install.
With the panel out of the way the blower speed controller is right in front of you as seen in the next picture.
Unplug the harness connector to get the blower motor to stop blowing. If you would like to see more details about testing please click here . To change the controller simply remove the two attaching screws with 5.5 mm heads and disconnect the remaining wiring from the blower motor.
This is a side view of the connector to the blower motor. The tab with the hook on the end has to be depressed before it can be pulled from the blower motor.
This picture shows the clip that has to be pushed in to release the three wire harness connector from the blower speed controller. It is a good idea to check the terminal spring tension in the three wire connector. To see and easy way to do this please click here. If your harness connector is damaged and needs to be replaced with the most updated part, please click here.
Install the new blower speed controller and reinstall the hush panel. This part number and design have been updated by General Motors. If you would like to see replacement information on installing the newly designed part please click here. If you would like to order this part please click here. If you have a cabin air filter now would be a good time to change it. This truck did not have one. If it did it would have been just to the left of the controller.
One last thing that I like to check is the a/c drain tube to make sure it is present and clear. If it is restricted it can cause water to build up and the water can damage the blower speed controller. If it is missing , water will not be completely diverted away from the cab and will make its way back inside and wet the carpet.