The HVAC blower motor may stop working at one or more speeds due to a faulty blower motor resistor block. Our technicians recommend to confirm the resistor is at fault by first checking the operation of the switch.Google+
Car Problem Reports
GMC Sonoma AC Blower Inop Due to Failed Resistor
GMC Sonoma Problem
Average Mileage: 125,333 mi (110,000 mi - 145,000 mi)
It is as if the AC stops working. But this problem shows up in the middle of summer when I am using the AC the most. I just stop getting cool air and then there is no air blowing through the vents at all. Not much I can do but turn everything off and roll the windows down.
Setting I and II wouldn't work. Replace Resistor to fix.
Visitor, 2000 GMC Sonoma, 145,000 mi
HVAC Blower motor works at 1,2,3 and fails on number 4 setting