Just picked up a C2500 Suburban, 2004. It has rear AC (with the rear and front ceiling-mounted controls). There are two issues:

1. Front blower works on all but #4 speed and also is "whiny" intermittently. Is this simply a blower motor replacement or something else?

2. Rear blower motor is not working. I hear the relay click on when I turn the fan control. I checked the front kickpanel connection, no melting/scarring. There is 12v at the back on the primary power circuits and 11v on the control circuit when the fan is turned on. However, there is no 12v output from the little control module in the back to the fan. Does this mean I need to replace that little module?

Thanks in advance!

 

Whiny blower motor could just be need for replacement. Operation on all but highest speed might mean to test the blower resistor module.

 

Some systems use a separate relay for high speed. Need a diagram to check it. Found that out on my old '09 Malibu with manual HVAC.
Looks like rear module may be dead. Shop manual will have it's diagnostics.
Alldatdiy.com is who I use for my fleet's manual needs.