im having a issue with my 2000 Tahoe. The rear blower isnt working currently. What ive done so far 1. checked fuses 2. rear resistor was burnt between the big orange wire and purple signal wire I replaced it. 3. getting 5v at resistor signal wire, getting 5v at center control unit signal wire input getting 5v at the front control unit signal wire. if i operate the front control unit speed control the voltage lowers as speed is turned down. If i ground any of the purple, purple white signal wires the blower turns on full speed. I thought it could be the middle overhead control unit so i replaced that with one from a salvage yard (still not working) i replaced the front overhead control unit (still not working) Both old and new control units operate the blend door and air direction servos as they should. This is a LT with the variable speed automatic climate control. Im figuring this system works off the 5v signal and goes to ground in the control units via electronic reostat, where zero resistance is full on, and as the resistance increases fan slows down. What can i try next fellas?
edit: ohmed out ground wires at both units and they are getting continuity to body ground so grounds are good

 

Do any of yall know if this system is connected to the body control module (BCM) or is it a stand alone unit with the center controller as the main brain?

 

Fixed it. The rear overhead unit was toast. i purchased a used on but it was also fried. i ordered a new unit and it all works as it should.