Could be a faulty fan motor and/or switch.
if this system uses dex-cool flush the system
yes or computer
Check for vacuum leak or bad vacuum motor Check selector control
Switch problem? Cables disconnected?
If you mean the fan works on high only it's the blower motor resistor.
Because the other one is damaged. Usually water damage.
The blower motor resistor is defective.
needs new blower resistor
Try replacing the temperature control switch for the rear control cluster. Hope that that's the fix. Less than $20.
The 2004 Chevrolet trailblazer air conditioning fan switch has three settings. The switch can malfunction, and only work in the high setting.
The system that controls the flaps that direct the air is not functioning.
blower motor resistor is bad