Had similar problem last month It's the Blower Motor Resistor that has gone. You can find it at the dealer for about $50.00 for oem chevy Remove the plastic cover under the passenger side dash, and you will see the plug connected to the resistor, and two other cables going towards the front of the car (Red and Black) which is the output to th fan. Remove the two screws (5.5metric) and pull the resistor out (make sure to unplug the connector to the resistor and the other one going to the fan.) Inspect your resistor for any burn marks (including on the Pins that go to the connector). Turns out that for my Resistor the Ground had burned and I could physically see the burn marks on the plastic for the resistor and on my plug (the ground had melted completely through). I had to get both the plug and the resistor replaced. I found the plug at the junk ($30). I just cut the old plug, and crimped the new plug to the existing wires (same colors). If not, you can always go to the dealer and pay the $100 + dollars for the plug, plus the install. I did this myself, for $80.00 and my fan works great! I got the Resistor on Ebay for $20.00. Anyways, if you go the DO IT YOURSELF way, make sure you buy some cable crimps (14-18G) that have heat shrink on them so you can connect the cables and have a nice tight seal around the crimps. Anyways, you run into any problems, or need help on something feel free to ask me by PM me.My heater - A/C fan only works on high (#5). Any other setting and it is off. I have heard that there may be a rheostat or something on the back of the blower motor that I may be able to replace to fix this... Any advise would be most appreciated!