HVAC Programmer

1995 Bonneville SSEI with auto temp control. Fan blower runs only on Low. Replaced blower control module with no help. AC repair shop says its the HVAC Programmer which costs new around $600. Any info on GM part # and location (I believe in dash somewhere) would be helpful. Also would there be difference in other GM models? The Blower control was the same but I'm not sure about the programmer. Then I can search for used parts. Any info about where GM part numbers can be found on line?