2006 Tahoe. Where is the auxiliary blower motor located?

Probably something going on with the blower motor control Processor . Hooking a scan tool an checking for DTC'S - diagnostic trouble codes would be the first step in a diagnostic procedure for a problem like this .

Auxiliary Blower Motor Control Processor
The auxiliary blower motor control processor is an interface between the auxiliary HVAC control module and the rear blower motor. The auxiliary blower motor control processor monitors supply voltage and ground circuits to the rear blower motor. The auxiliary HVAC control module provides a pulse width modulation (PWM) signal to the control processor in order to command the blower motor speed. The auxiliary blower motor control processor uses the blower motor ground as a low side control to adjust the blower motor speed.
The blower motor forces air to circulate within the vehicles interior. The vehicle operator determines the blower motors speed by placing the blower motor switch in a desired speed position or by selecting automatic operation. In manual operation, once a blower speed is selected, the blower speed remains constant, until a new speed is selected. In automatic operation, the HVAC control module will determine what blower speed is necessary in order to achieve or maintain a desired temperature.
As the requested blower speed increases, the following conditions occur:
• The HVAC control module increases the amount of time that the blower motor speed control circuit is modulated to ground.
• The voltage and duty cycle, measured between the blower motor speed control circuit and ground, decrease.
As the requested blower speed decreases, the following conditions occur:
• The HVAC control module decreases the amount of time that the blower motor speed control circuit is modulated to ground.
• The voltage and duty cycle, measured between the blower motor speed control circuit and ground, increase.

Fuse for rear air ????? No air coming from rear vent's ? That would be caused by the HVAC blower motor not working . Probably not a fuse issue , if the fuse is blown you have a bigger issue . Fuse's don't just blow for no reason - electrical short circuit, too much current draw etc.. . More then likely it's a problem with the blower motor control module or the blower motor . Located behind the right rear trim panel . But go ahead an check the fuse anyway , fuse # 26 - 25 amp located in the underhood fuse / relay box . marked RR -BLWR/ 110 VAC
Auxiliary Air Speed
The auxiliary blower motor is controlled by the front auxiliary blower motor switch. If the vehicle is equipped with rear DVD (U32), the auxiliary blower motor can be controlled by the overhead console, vehicle entertainment system (VES). The front auxiliary blower switch must be in the AUX position in order to control blower speed from the VES. The VES will send a class 2 message to the HVAC control module requesting a blower motor speed.
The auxiliary blower motor control module is an interface between the HVAC control module and the auxiliary blower motor. The auxiliary blower motor speed control, auxiliary blower motor speed signal, blower motor speed control, and ground circuits enable the control processor to operate. The HVAC control module sends the commanded blower motor speed to the control processor through a 0 to 8-volt linear ramped blower motor speed control circuit. As the blower motor speed control voltage increases, the blower motor speed increases. The control processor sends the actual blower speed to the HVAC control module through a 0 to 12-volt blower motor speed signal circuit. The control processor uses the blower motor ground as a low side control to adjust the blower motor speed. The underhood fuse block supplies 12 volts to the blower motor through the blower motor voltage supply circuit.

RR/HVAC fuse 30amp located in the under hood fuse box. You can check it but highly doubt it's the problem . More then like it's the blower motor control module that's bad .
Circuit/System Description
The auxiliary blower motor is a variable speed fan. The HVAC control module controls the fan speed by sending a pulse width modulated signal to the auxiliary blower motor control module. The auxiliary blower motor control module varies the duty cycle across the auxiliary blower motor in relation to the pulse width modulated signal. The auxiliary blower motor speed can be adjusted from 10 percent to 90 percent duty cycle (PWM), 90 percent is high speed fan.
Watch this video for testing purpose's only , this is a front blower motor control module . Same way your back one works . GM is GM Chevy , Buick ,GMC , Cadillac .

Doesn't it work in any speed ? Could have Blower Motor Control Processor if yours has automatic HVAC .
Or if manual it has blower motor resistor . Both are located under passenger side dash . Remove insulator panel under the dash if it has one !
ORO How to replace blower motor resistor in Chevrolet Silverado

2005 Chevrolet Tahoe Blower Not Working

There usually isn't a separate one for the rear. You may have a bad motor in that blower. Some blower assemblies have a resistor on the housing assembly. Try jumping the motor first to see if it works using your car battery.

Yes there are some fuse involved in these systems. Does your vehicle have manual or automatic temperature control , there are a lot more electronics in the automatic system. Do you feel any air coming out of the rear vents ? Do you here the Auxiliary Blower Motor running ? if you place the auxiliary blower motor switch in each speed position does the motor run at all.? If the blower motor doesn't run you probably have a bad blower motor resistor.

Hi!!
Look ion the INSTRUMENT PANEL Fuse Box, there are two blower motor relays and two fuses, look on the inside of the relay cover for a diagram. The relay you are looking for should be labeled FRONT BLOWER MOTOR RELAY and the rear one should say AUXILIARY BLOWER MOTOR RELAY.
The TWO fuses with the same name on passenger compartment fuse box check:

• fuse #39 30A fuse. AUXILIARY BLOWER MOTOR
• fuse #36 30A fuse. AUXILIARY BLOWER RELAY

Sounds like the blower motor resistor. It's located under the dash on the passenger side of the vehicle just behind the blower motor itself. It's a fairly easy job to do. Just replaced one on my own truck. Good luck :)

looking to LR (left rear) Passenger Compartment , you're truck properly bad (air temperature actuator / auxiliary) located next to blower motor

See http://www.sparkysanswers.com/labels/Blower.html, Sparky has all the information that you will need. Great help.