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.
If you would like to see a video of a similar repair please click here.
More than likely the blower speed controller is faulty. A quick check with a voltmeter as outlined in the articles should prove this out. It is very common for the blower motor to stay on when the key is off when the blower speed controller fails. The pulsing that you felt is also a normal thing in that the blower speed controller uses pulse width modulation of the ground circuit to control the blower speed. The part has been updated by GM and AC Delco and looks a little different. I am including a link to another article about the new part.
http://www.sparkys-answers.com/2011/07/2003-gmc-yukon-bower-erratic-not.html
Sparky, i took some readings on my blower control module formy 03 silverado but looking at ur other links for testing i wasnt sure if they were for the new module or oem original. My readings are below starting from the highest setting and working down.
Red wire and purple: 9.3, 8.2, 7.43, 6.95, 6.58, 6.3, 5.97, 5.66 volts
Purple and black: 1.72, 2.65, 3.4, 3.9, 4.25, 4.5, 4.83, 5.13 volts
This is for a digital auto climate set up which my fan controls dont change anything and fan not shutting off when power is off.
Some great articles on this situation however i seemed to be more confused now that before. I have an 03 silvy with auto control and for a while now I only had low speed for the fan. Occasionally it would kick onto high speed. Started pulling things apart and noticed if i pulled the fan housing out and turned on my controls to high it would stay at a low speed unless i held onto the fan for a few seconds and it would pulse then kick to high. Once it hits high speed it will not go back to low speed and I have to pull the plug as it will not shut off either. All the terminal looks fine and no burn marks or anything. This all started after a dead battery about a year ago. Any ideas? The two issues with fan speeds and not shutting off all seem to be conflicting with each other.
Thanks,
Disconnect the HVAC control head wiring and the five wire connector at the new blower speed controller. Check the small purple/white wire for a short to ground. With both ends disconnected there should be no continuity to ground.
I have replaced the control module, blower motor resistor and blower motor. Blower will not stop running unless I pull fuse. All parts purchased were AC Delco from dealer.
I had to wire in new harness, 3 wires.
2003 tahoe with auto climate control.
Same problem with a 2003 Chevy 2500Express. Be advised, the part is under the hood in the engine compartment in that type vehicle, not under the dash. Pull the 40A blower fuse until you can get it fixed. If you can’t do it yourself, get an independent A/C guy to do it, not the dealer unless under warranty.