I have a 2000 buick century custom. To give a little background, the fan speeds would all work except for '3' and that lasted for about 4 months... then it came back and was working again, and now none of the fan speeds work, so its 20 below and i have no defrost... When i switch between vents i can feel the smallest amount of hot air leaking out... Checked for fuses and could not find anything blown... any suggestions would be greatly appreciated.

 

Sounds like a bad blower motor relay. It's located on the blower motor, behind the glove box.

 

Your fan motor is shot. Replace it and you will be warm in no time.

 

century 2003 overheating and heater throwing cold air