This 2003 GMC Yukon came in with the complaint that the blower was doing weird things. The blower sometimes would not turn off when the ignition was turned off. Also sometimes the blower worked and sometimes it did not. Withe the local temperature expected to top off at over 100 degrees F and the the index expected to reach 120 degrees F, the customer said it had to be fixed. I agree.
The first step is to remove two of the three 7 mm screws (center and right hand), that hold the hush panel on under the passenger side of the dash.
With the hush panel dropped down, it is a quick test of the wiring, click here to see that information. The two most common failure symptoms with this part are an inoperative blower motor or a blower motor that will not turn off even with the key off. For testing information please see these repair articles. 2003 Chevrolet Silverado Blower , 2004 Chevrolet Silverado Blower Will Not Turn Off. and 2005 Chevrolet Tahoe Blower Not Working (video).
Using a screw driver or similar device, depress the locking tab and disconnect the wiring to the blower motor.
Remove the two screws holding the blower speed controller in place.
Push in the locking tab and disconnect the three wire connector from the blower speed controller.
Install the foam spacer on the hole marked 800 on the end of the unit that has four holes.
Mount the blower speed controller using the supplied screws. You will be using the mounting holes marked 800 on the new unit. Note the foam spacer under the left mount in the picture below.
Install the new wiring into the blower speed controller.
Connect the harness to the blower motor.
Cut and splice one wire at a time. Stagger the joints so that the wiring harness will be neat and trouble free.
Remove the BLWR fuse in the under hood fuse box before cutting the red wire. You might be tempted to disconnect the battery instead, but I do not recommend it. The act of disconnecting the battery does two things that can be detrimental: 1) Loses learned memory, which could result in a poor idle condition, and 2) Starts the recalibration procedure for the HVAC actuators, which may result in stuck HVAC doors and more expense.
Wrap tape back around the harness and put the hush panel back into place. Keep in mind that the old part number 15-80567 is no longer available and it has been replaced by this new kit. If you need this blower speed controller kit, please click here.
Another one done.
I decided to do some updated testing due to the design change by GM. There is still a constant 12 volt signal on the Red wire and constant ground on the Black wire.
Things have changed on the purple wire though with the new blower speed controller installation. One can test from the red wire to the purple wire or from the black wire to the purple wire with your voltmeter. GM recommend’s checking from the red to the purple but I prefer checking from the black to the purple. My reasoning is that it educates us that the blower speed controller has a nominal 12 volt output on the purple wire that the a/c control head signal brings down by applying a pulsed ground signal to. The chart starts at the highest blower position and descends one notch at a time to the lowest blower setting.
Red wire Purple wire Black wire Scan Tool Duty Cycle
8.57 volts Highest Speed 4.65 volts 78%
6.65 volts High -1 6.75 volts 59%
5.10 volts High -2 8.50 volts 43%
4.08 volts High -3 9.65 volts 33%
3.27 volts High -4 10.52 volts 25%
2.71 volts High -5 11.15 volts 20%
1.98 volts High -6 11.95 volts 13%
1.32 volts Lowest Speed 12.64 volts 6%
Keep in mind that the voltage is due to the duty cycle of a switched ground from the a/c control head. In bench testing I have confirmed that applying a constant ground to the purple wire will only yield a single pulse from the blower motor. Repeating the applied ground multiple times in a short period will allow the motor to run. I do not know if this added info will help anyone or not but I thought it was at least interesting from a technical perspective.
There is a new development in this repair. It seems that General Motors has added or changed a circuit in the new module that reduces what they refer to as “Thermal Events”. In doing so the new module does not always play well with aged blower motors. What we wind up with is this. The blower motor will not work on an engine restart unless the a/c controls were switched off before the ignition was cycled off and back on after the engine is running again. The two immediate ways to address this issue is to learn to remember to cycle the switches in the above manner or replace the aged blower motor with a new one. I suspect there may be a software update somewhere down the road but that will require dealer level programming abilities. Since the replacement part is only available from GM or through an ACDelco distributor we are all being subjected to this problem.
There was not a software update but another part is now being supplied and so far with no unexpected issues. Click here for the new product link.
The latest design ACDelco part is distinguished by being a light gray in color.