This 2004 Chevrolet Tahoe came in with the complaint that the rear blower would not turn off and the battery went dead as a result. This Tahoe has manual a/c controls. The first thing that I did since the vehicle had to be jumped off to get it to my shop was to turn the engine off and install a battery charger. While the battery was charging, I started checking things out. I located the RR HVAC fuse in the underhood fuse box and pulled it out. I show the fuse location at the end of this post. The fan turned off and I went to print out a wiring diagram of the system. When I came back to the Tahoe with the wiring diagram, meters, and basic 1/4″ tools, I installed the fuse and the system was now working correctly…well, almost. I noticed that there was no high speed unless the switch was rocked back and forth. Almost like there was a “sweet spot”.
I checked that condition and it was the same at the front or rear switch panels. Not likely that both switches failed in the same way at the same time.
I continued to the rear of the Tahoe to find the blower resistor assembly. The diagram showed that it contained three relays and a resistor assembly. It also showed its location behind the right rear interior panel.
To remove that panel, the related trim panels have to be taken off first. The floor trim panel lifts off with a little bit of force.
Then the ceiling trim panel comes off in the same manner.
A close up of one of the retaining clips.
Then the right rear pillar panel. I started at the top and worked my way down.
This Tahoe had a speaker that had to be disconnected.
Now the cargo net retainer. It unscrews but I had to wrap it with a rag and use a pair of smooth jaw pliers to break it loose.
Then the push pin retainer.
I could then pull the panel back far enough to work.
Testing goes as follows:
Four wire harness connector:
Terminal “A” Black wire is a constant ground.
Terminal “B” Orange wire has a constant 12 volts power supply from the RR HVAC fuse in the underhood fuse box.
Terminal “C” Brown wire has a 12 volts switched ignition and is an output from the resistor. Meaning that it will only have power on it with the key on and the resistor harnesses connected. It’s power source is terminal “D” of this same connector and it sends ignition voltage to the rear mode and temperature door actuators.
Terminal “D” Brown wire* has 12 volts switched ignition supplied through the IGN 3 fuse in the left instrument panel fuse box.
*By the wiring diagram the wire color should be brown but in the vehicle it was brown with a blue dot.
At the three wire connector:
Terminal “A” Dark Blue wire is switched ground for low speed.
Terminal “B” Red wire is switched ground for medium speed.
Terminal “C” White wire is switched ground for high speed.
Testing for a switched ground should be done with the harness disconnected from the resistor assembly. If you were to test with the harness connected to the resistor and the key on you would find power on all three wires with the blower switches placed in the off position. The power would be bleed through voltage through each relay coil. Near zero volts would be present on any one wire that was in the switched ground position.
All of the signals were correct so I installed a new resistor assembly. Two 7 mm screws held the resistor in place. I also did some checking and found that this resistor and repair procedure will apply to 2000, 2001 2002, 2003, 2004, 2005 & 2006 Chevrolet Tahoe and GMC Yukon. It also applies to 2002-2006 Cadillac Escalade. If you need one of these resistors please click here.
Now I will admit that testing is a bit awkward with the main cover panel in place but to fully remove the panel the right rear seat belt assembly has to be removed. The right rear floor trim panel has to be removed and the pillar panel also has to be removed.
In the picture below I point out the RR HVAC fuse located in the underhood fuse box.
The underhood fuse box legend.